Score! What did I do?

Both of my 66 Darts 2bbl & 4bbl had solid lifters. If you have adjustable rocker arms in working condition (none of the adjusters stripped out )on your 273, stick a mild cam and new lifters in it. You'll get a good daily driver out of it.

The Poly 318 will physically fit, but.

1. There are no exhaust manifolds made for the A-body.
2. The reason for the LA design was to make a lighter, smaller engine that would permit an underhood exhaust system to be fitted. I think I read that the 273 weighed in 150 lbs less than the 318 Poly and only about 50 lbs more than the /6.