I'd just wait untill you get the rifle and shoot it some. Adjusting the "irons" elevation will give you a good idea of how much droop your barrel may or may not have,....also a straight edge will help you to evaluate which mount you need,...be it the UTG 34, 46,. or the non compensating rail they offer. Ring heighth (SP?!?!) is totally dependant on the shooter. I put the 34 rail on my,..34!!! And it works great. My B-28A has no droop to merit a comp mount,..so I chose the Non-Comp rail for it,...Again,....excellent results and performance!! Like I said, Wait until you get the weapon and shoot it some. Then you'll get a better feeling of which route to take,...Mount/rail wise. tjk