i run a 4.3 with 700r4 trans in a 4 door 1946 plymouth, i get 18-20 mpg. i converted mine to a 500 cfm carb from factory tbi( it was shot) dyno's at 203hp. more than enough power for around town and 80+ mph on the freeway.

daren

1952 GMC 1-Ton
1946 plymouth
1947 ford
custom builder
http://www.doublegcustoms.com