Ive got a thing for 5.56 AKMs. The SAR3s are pretty decent and have some advantages over other choices. They are surprisingly accurate - likely the Bulgy barrel. As above, very reliable with decently priced, available mags (Wieger - Interordinance still have any?).
On the other hand, they have crap, poorly fitted internals (easy fix as above). Finish, wood and metal, leaves a bit to be desired and often issue with canted FSB. Refinish or grab a stock set get some Norrel moly and fix the cant. If you're not careful tho, you can wrap up the cost of a SA M7 or built AK-102 - which might be a better buy. Least those two pedigree better - tho milled SA is no adv to me. They are no longer imported, but plenty around.
The barrel should roughly measure .50 inches. Easy enough to thread 1/2x28 - AR15 pitch, so you can use AR flash hiders. Vortex dont look bad, but you can score adapters for other more AK like FH.
Heres a source for threading kits. Someone on the EE rents them as well.
dynasystems-ltd.com/threadingkits.htmLuck
Alac
Edit - I still need a Beryl