Ya we didn't know it when I got it but we found out. "It kinda helps when my dad is a mechanic and my grandpa was a mechanic and my ex-girlfriends dad was a mechanic. They are very hard to find. They aren't worth getting a BB from a SB for a average driver because not enough extra power for how much more gas it uses but for what I do it's alright. " We load trailers with scrap metal and other things pull boats and you can't even tell there is something behind you. It actually drives better and runs better because it puts a load on my transmission and rear end.
Term, I really don't get what you're saying. A Chevy engine that displaces 350 cubic inches will be nearly identical in milage, no matter if its a small block or a big block... provided the BB had a similar fuel setup as the SB. Displacement is displacement. A heavier crank and/or heavier rods would make an engine slightly less efficient, but not terribly so.
GM produced a BB engine that displaced 366 cubic inches from the '60s until the mid '90s. The engine was used in medium trucks (Topkick, schoolbuses etc). Could this be the engine you have?
Short stroke engines have greater HP than Torque. The longer the stroke on a given engine, the greater the torque, but the lower the HP.
SB 350Bore: 4.0"
Stroke: 3.48"
BB 366Bore: 3.935"
Stroke: 3.76"
In order to displace 350ci, the stroke would have to be reduced to 3.5", a loss of .26".
BB 454Bore: 4.251"
Stroke: 4.0"
In order to displace 350ci, the stroke would have to be reduced to 3.08", a loss of .92".
Neither of these options seem very feasible to me. In addition to being a lot of work, both of these scenarios would result in an engine that has theoretically LESS torque than a SB 350. Why would anyone go through all that trouble and spend all that money on custom machine work for a loss in torque? Granted, a short stroke, large bore engine could make some serious horsepower and rev really high, but in order to utilize that potential to its fullest, the engine would likely need an FI setup (ie supercharger or turbocharger).
See why I want to see a picture of your engine? I'm really curious about your truck. Seems odd to me that someone would go to all that trouble for a crappy engine when they could just put in a stock 366 or 454 and call it a day.