1966 Dart 225 Slant/3 spd power/MPG?

On another forum I mentioned that I have a lead on a 1966 Dodge dart locally.

Car has a Slant Six (probably a 225) with a 3 spd on the column.

Clutch is history and such being the case; I plan to bolt up an all synchro 3 gear from a 1970's A-F-M body to do away with the 'crash box' low gear transmission.

I do want to leave the motor stock outside of an electronic ignition conversion.

Remember that I plan to pitch the 13" wheels for 14's when I swap on 1973+ disc brakes and matching bolt pattern rear end.

Realistically; what can I expect for MPG in average driving and for approximate 0-60 MPH acceleration times?