1975 904 for slant 6

What is a good converter to get for stock 198 slant 6 ? Stall and diameter I see 10&11 inch . Not looking for any performance . Just good for cruising and lots of highway trips.

Not the same car this 1975 2 door dart if you must know . It's green , it has 4 15" wheels .

I work on lot of projects that aren't my own cars.