thanks for the replies, and the old 305 probably uses a quart in 700 miles.I used it for a week driving 120 miles each day round trip hauling a welding machine bottles etc on a skid I built to slide in- I stopped at the same station each day and it held 10 gallons to top ooff so it gets an honest 12. has an aftermarket holley 2 bbl. that was kinda grungy but I cleaned it up. and I doubt the 454 would beat it any on mileage. it has the old GMC rear end that checks to be 4.10 ratio. I would not do more than an engine swap and at this point it probably doesn't make sense unless it's just to say I did. doubt I'd gain mileage and might even be worse with no overdrive. just a straight truck 4 speed.I do know of the fellow that built the engine so I would not be concerned it it checks out OK. I can run it in the truck it's in.but I'm not going street rod with it and better keep what bucks I have