I just measured two M1 front sights, one on my "as issued" M1 and one on a new, never installed sight.
The front post is .215" high.
This puts me 8 clicks up from the bottom to be on at 100 yards. This is using the 6'O'Clock hold on the NRA 200 yard target reduced to 100 yards.
So as Bart said, measure your front sight and compare to what the new sight.
Don't screw with the rifle until you determine the height of your existing sight.
CPT USAR Ret
USAMU Sniper School Oct '78
Distinguished Rifle Badge 1071