I put a vintage air R134 a/c system in my mid 80's CUCV blazer many years ago. It would do ok for the front but not for the rear seating, and I did a pretty good job of insulating, sound deadening and window tinting. Maybe their system has improved.
Before you have the driveshaft lengthened take the cap off the end of the yoke and check the condition of the seal/packing. If needed change the seal/packing clean the old grease out and pump some new grease in until it leaks out the weep hole near the u-joint. Then have the driveshaft lengthened.
Did it run ok before you did anything to it? Did you do any valve adjustment?, Have or can you do a compression and/or leak down tests? Correct firing order? Do you have a service manual with a trouble shooting section?
The dowels are the same, I am not an expert but, I don't think a bellhousing for an 10.5" clutch will fit over an 11" clutch. Also, have you tried the fitment without the starter in place?
My old '84 and '93 K30's were both 6 tire one ton's and had the style wheel you've pictured front and rear & used the ring. The '93 has 14mm studs and lug nuts that are set up for hub caps.
I use a minute mount 1 during plow season on my bobcat 873 skid steer. The plow has its own battery and charges thru an isolator that most likely came from amazon (P/N BTI-140) 12v 140A. After three winters nothing has caught fire or exploded yet.
No, I've replaced the flex plate by sliding the th400 and NP208 back on long 3/8" bolts, of course after disconnecting crossmember, driveshafts, lines, linkage etc.