I am trying to finish up a project and I am curious on the journal sizing of two fsb/gb that kvar sells. My barrel is .590 at the gas block, will either of these combos work? Ive sent an email off to kvar, but I havent had a response yet.

ak-142b
kr-008b

For one, each of those sights are different. One is for a AKSU and the other is for a AK 105 type rifle (or Bulgarian "CR") There is a sight tower height difference between the two. The AK142 can use a standard rear sight  to work with it, while the KR008 needs a krinkov hinged dustcover sight.
Aside from that, I know the Bulgarina AK142 is ~.590 in diameter and is suppose to go right where the standard 90degrree gas block is on a Bulgarian 74. The gas port hole should line up and the diameter should be correct. This info can be double checked by doing a google search.