/6 rebuild advice

SoCal mopar said
I just purchased for relatively cheap, a 2 door, 72 Dart /6 255, automatic 3. Car had been sitting for years before I got to it, supposedly :BangHead: oil looks good, brakes work good, no ticking, dies at a stop sign (what ever), points not electric, and is a vacuum nightmare, front end needs everything of coarse ......all things I can do....

Looks like the rear main seal is leaking which I am hearing is a small project.... easier to remove the engine to fix...... and taking the car for the longest drive I've done yet, it over heated....... cooled off fast, and while topping it off with water to get home I noticed it had a milky, foamy, substance ? in the radiator neck .....

I have a 318 sitting in my garage.... but.... knowing swaps aren't always/ever direct swaps/easy, would it be CHEAPER/easier to rebuild the 6 or put the 318 engine in, in its place?

My first /6 car..... I only want a reliable fun driver, nothing hot......

Thanks in advance.

Any solid or recommended mechanics in the Thousand Oaks / Camarillo areas in SoCal would be nice.

My vote would be to repair the 6. You could put in a mild cam and the Super Six 2V intake. Split exhaust manifolds like Dutra. Use an X pipe to keep the noise down. Rusty would be a good one to listen on the slant.
Seeing as how the foam is gone, probably a good idea to replace the thermostat and drive it.
When doing a compression test, 4 or 5 hits on compression should do the job. The first 2 should get about 90% of the final after 5 compression strokes.