How to turn a half ton into a 3/4 ton?

I have a K20 truck with a very rotted floor and floor framing and there's a half ton for sale with a good body, what would i have to swap out to make the half ton a 3/4? I'm thinking the rear springs and differentials, anything else? Thanks

The frames are completely different, the half ton is smaller/weaker. You'd be better off just swapping the half ton body onto your 3/4 ton frame if you wanna keep the 3/4 ton usage

*I had a brain fart, editing for good measure. I was thinking of the C6P option that gave the heavier duty frame.

I read on. a sticky somewhere, maybe this forum, that the 10s and 20s are the same frame but the 30s are larger but not thicker metal. However I am more inclined to swap the cab out, probably just as easy or easier.

TotalyHucked said:

The frames are completely different, the half ton is smaller/weaker. You'd be better off just swapping the half ton body onto your 3/4 ton frame if you wanna keep the 3/4 ton usage

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A longbed K10 and K20 are the same frames, at least per GM literature for 1979.

Thanks, good to know my options

legopnuematic said:

A longbed K10 and K20 are the same frames, at least per GM literature for 1979.

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You're right, brain fart. I was thinking about the C6P trucks

Wouldn’t it be easier to keep your 3/4 ton frame, and just move the good 1/2 ton cab and bed over?

Moving the bed is simple, and moving the cab should not be much harder. The only complication is to make sure the cab is for a 4WD so that it’s has the high floor hump to clear the transfer case. Even that is fixable if the floor hump in the K20 is in good enough shape to cut out and move over. In some years I think that high hump was just bolted in, so it might be really easy.

TotalyHucked said:

You're right, brain fart. I was thinking about the C6P trucks

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My observation has been that the K10s have a perforated rear crossmember. I must admit, I haven't tried to find a non C6P K20 to compare.

But if the crossmembers are different, who knows what else is different? There's also the prospect of rear leaf spring length.

I would think there are builds here with pics:

long time ago I had a friend with a 1983 4wd 1/2 ton
with 3/4 ton axles on tall tires... it sat high like it has a 1.5" lift.
(did not go far with it, just 10-20 mile trips daily in the 3 warm seasons,...kept off the public salted roads in winter,

not sure what he did to make it that way, ...but he did drive it for many years,...probably still have it, but for a major engine fire that stunk up the interior. (I think sold whole and parted out after that)

Blue Ox said:

My observation has been that the K10s have a perforated rear crossmember. I must admit, I haven't tried to find a non C6P K20 to compare.

But if the crossmembers are different, who knows what else is different? There's also the prospect of rear leaf spring length.

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Some C10s do as well, at least my truck does

I'm not going to swap differentials but I'm willing to swap the cabs. If I do end up replacing the bad body panels I'll take my cab off first and lay it on one side at a time on tires and weld standing up. As I recall both sides need inner and outer rockers and some floor and those short supports underneath. But the rest of the body is good. The floors rot from the snow from the boots, but it's pretty dry here. So thats how I'm probably going because I just got reminded that it might not even be legal here to swap cabs since the VIN is on the cab. I may go down to the courthouse and find out. The other thing I've been wondering about lately, regarding other upgrades is the fact that my insurance company asks (every time I add a vehicle) if I have done any modifications to the truck, I forget how they say it but it seems to let them off the hook if I do any conversions at all. I may ask an insurance agent about that. They sure do look for sneaky ways out of a obligation if they can work it
On the other hand, if all I had to do was swap those diffs, that might be the easiest way to go. Ill measure the springs on the 1/2 ton

at this age,...I would think all that is required is, a clean title vin plate has to be mounted on a cab, and a clean title for that vin # has to be in your hand.

and if anyone hunts at a special inspection,...what they are looking for is stolen parts,...and cab vin #s that were floods/ wrecks that are branded as Not Rebuild-able.

Might be better off just dropping a complete floor pan in it over buying a whole truck and swapping cabs and possible title issues

Thanks but I already priced the parts I need and it comes to about 300 from LMC. The one piece floor is 770. It's not that much of the floor pan, its also the rocker panels inside and out as well as some of the square tubing underneath the floor butting to the rockers. Ill get a picture of it up. It's left and right sides. When you get melted snow puddling its mostly in the two outer forward corners that's going to rust. Carpet really holds it in and keeps it from drying out but I've got rubber on this floor. Probably original. If owners would just put a coat of linseed oil or wax-oil on their floors once a year there'd be a lot more squarebodies in the world today
If you take the whole floor pan out you also have to brace the cab so it doesn't move out of square while you replace it.

I would look at TABCO for parts. They claim to be US made or use domestically produced steel. If nothing else their metal is a thicker than any other supplier I have used. I used them last summer to redo the drivers side rocker (inner/outer), cab support and cab corner. Pretty nice stuff to be honest. For your cab/VIN/frame concerns, I sometimes think there are more mish-mashed cabs & frames out there than there are non-swapped trucks.