I was thinking of rebuilding a 350 to 383 but was also thinking of the ls1/lt1 swap If I rebuild a 350 without FI can I get decent mpg? What will the total costs (est) be for a conversion?(All work outsourced). I am looking at it from a reliability standpoint as I hope to come down to the USA and see some of these huge car shows...

I can wrench so that isnt much of an issue for minor things.

As a note I am looking at 400 hp/tq

What kind of car and what mileage do you consider "decent" ? My 1985 Blazer would get 20 mpg highway with a mild 350 and a q-jet carb. This was through stock exhaust.

1971 Chevelle Convertible

I am trying to get a nice driver to travel cross country and to light them up when im local :D hence why 400/400 hp tq and decent mileage sure i guess 20 mpg would be decent. Does this sound reasonable and with which combo?

I dont know tranny/rear as of yet need to pull the codes off because the tranny isnt original. I know its a 4 spd (maybe from a 73?? dont know what :D)

Get the newest & best you can afford. Forget the 4-speed, get a T56 6 speed. An LT1 from a Craprice, Roadmaster, or Camaro would be cheap yet good, but an LS would be better, and the LS will definitely give you better mileage. BTW, EFI is not the only way to gas mileage. The good 'ol Q-Jet is hard to beat, and you can easily tune it leaner on the Primaries. Another neat trick nobody knows about is the Offenhauser Dual Port manifolds. There are some neat tricks you can do with one of those.. (IM me if you're curious about that)
I had a 406/dual port/700r4/3.31 in a 4000 lb car that got mileage in the mid 20s & would run with the new (in about 1990) Corvettes.