No doubt the earlier 250's were MUCH better than the post '75 era ones up until '84...the integral head design sucked,though it did increase HP and torque a tiny bit..it forbid you from ever putting a custom intake or headers on them,and though you could swap the old design head on them,they tended to overheat because the coolant ports were not exactly the same..had to use the old style gasket and it partially blocked the coolant passages..
I have owned three of the 250's with the "integral head",one was a '75 in a 2wd K5 that had a one barrel carb,it always had a lean surge no amount of carb fudgery could completely cure,but it ran good otherwise and I used to commute 60 miles a day each way to work and back for a good year with no issues..thing got 17 mpg ,I put a saginaw 4 speed from a '75 Vega in it in place of the original 3 speed...one day coming home from NH the fiber cam gear let go 3 miles from my house!..that was about the only time I had to walk home after a Chevy let me down and get towed..
The other two 250's I had were in a 79 C-10 Bonanza and a '81 G-10 van..both had the integral head and the lousy E2SE Rochester 2 bbl that were actually half a Q-jet cut in half ,they were a suck pill to work on and neither of them ever ran that great--those check valves and smog pipes in the valve covers were a joke too..
I "deleted" all that crap and put 4 barrel carbs on them with adapters I made,I ended up not connecting the secondary linkages though,a 600 CFM carb was too big for that dinky an engine..they ran decent after the carb swap though,and though they were not speedy by any means,I liked the low end torque,eventually I did decide to install a 305 and a 307 in them,which was not really much of an improvement after all the effort and BS searching for the parts to do it..
I think if your going to go with a V8,you might as well go BIG and get a 400 SB or a 454,even a 350 is not always gutsy enough if its a smog era version in stock form,for a full sized truck...but in a Camaro a straight six does OK...
