How 'bout some more info like the intended purpose of the rifle?
The sight post
will be in the way...it's the nature of the beast. If you don't want to see the FSB, get a low profile gas block.
One other option, is to leave the FSB on the front and put a flip-up BUIS on the rear and
co-witness the sights.
At no more than 100, why don't you just put on a zero magnification red dot (EOtech/Aimpoint) and call it a day?
Seriously, you don't need magnification at that distance unless you're shooting competition, varmints, etc. If you want it just because, then go for it: red dot or low mag IMHO. Finally, in the last year or two a lot of manufacturers have been coming out with 1-4 with a tactical type feel. Might peruse
this link for more info.
For mounts, look at Larue. They make a mount for darn near everything.
If you're dead set on an ACOG, the TA11 is the best for competition (taking into consideration the awesome eye relief), while I prefer the TA33 with a bit more peripheral vision.