Is this gonna be like a full time daily driver, a backup daily driver, or something that you just take out once in a while? 305s aren't good for much, it's true. That's not to say they're not good for anything, though. Even though my Caprice is geared taller than the Empire State Building, I get about 23 MPG on the highway give or take doing a cruising average of 77 MPH. I'll drive it between my mom's house in Mississippi from New Orleans (2 hours) or my house on the MS Gulf Coast (1 hour) and it does well in that sense. It performs reliably and respectably when everything's working right and the timing's set properly. I wouldn't be objected to building it up, but I say that knowing full well that you get the same or less power with more time and money than you would in a 350. As mentioned, the bore and stroke of a 305 aren't as amicable to upgrades as some other versions of the SBC. I like the 305, myself, but that's knowing full well what the motor is made for, what it can do, and what it takes to make it do more. Plus, mine's an L69, which I would argue is the best 305 they made and just a hair above the truck version with the 601 heads. The LG4 305 is a piece of **** that lives up to the negative hype.
I like all the common Chevy inline sixes, Gen I V8s, and BBCs so I don't think there's a bad choice to make. I think it just depends on what you're looking to do with the truck. As far as transmissions go, I'd say a late model 700R4 is a great platform to build a transmission on for a 400 SBC or smaller. If you want a 454, I'd do a TH400 or a 4L80E w/ a standalone controller.
