[Nonhog]

I have a 66 Volvo 122 (Amazon) estate (wagon) its got a B20 Volvo engine that has promise. I know someone who gets 38 mpg with his.
My thought are what engine would be powerful enough to run an atm. and still get decent MPG 40 would be awesome but I could live with 30-35.
Swapping engines does not scare me. But spending more than needed does.
No dream builds, needs to be reasonable. And since its RWD platform no expensive adaptors unless its worth it in the long run.
The current set up according to the original owner got 25 MPG. No O/D.
This car has 4.56 gears factory to help the low torque B18 it originally had.

Ideas/thoughts welcome!