If you own a pre 1966 car/truck and you are only grocery getting, then 516 heads are FINE!
My grocery getting days in a Mopar are well and truly over for me...
I love Mopar iron heads and am always happy to spend an hour or twenty on them.
My own bug-bear' with 516 heads is, they ''break through' real easy on the exhausts, even with mild port work...
They have a bad exhaust port and that's how it is...
The 'Stan Weiss' Flowchart is mind-blowing and takes some reading!
516 Intakes around 220 cfm which is poor.
No 915 'raised port' flow numbers, but they are basically 'closed chamber 906's.
A very trick 906 intake will get you somewhere near too 300 cfm's...COOLIO...
So if you can get 300cfm with any head you need approx, 75% for the exhaust too...(225 cfm).
There is one set of stock '2.08-1.74' 906 heads with 250cfm flow.
If you can start with those numbers you are onto a winner lol...