Quoted: I am very interested in 308 AR type but would like to know what is the difference b/t the 2 lowers in regard to lower receiver parts? Can I (or will it work correctly) use a DPMS AP4 upper on an AR10 80% lower if some modification is necessary to use the DPMS mag? Is the magwell differ on the DPMS / SR-25 than on AR10?

Many of the parts interchange, but there are some special parts.
Bolt catch and takedown pins are different for sure, at least the rear takedown pin is.

The major thing keeping you from putting a DPMS upper on an Armalite lower is the radius leading up to the buffer tube threads.

More info & a picture here: www.ar15.com/forums/topic.html?b=3&f=121&t=265951

The magazine wells are completely different.
Armalite is one way and DPMS/Stoner are the other.
They are not going to interchange easily.
If you are starting with an 80% lower, you could simply mill the readius into the lower to take a DPMS upper and an Armalite upper should still work as well, but with an ugly gap.