Darrell's Scout Mounts are the only way to go and he makes various mounts for assorted Mosins and other rifles. The mounts are good no they are the best! I have one on a M38 Mosin and it has been rock solid unlike a B-Square I tried first. His products are top quality, yes they may cost more but they work!! IMHO!!!
I've used the weaver rail version because i had weaver rings and they were the lowest ones - just what i needed.
I've also bought their No 4 Mk1 rear sight mount and very happy with it. Although, No 1 Mk3 (receiver mount) that i bought didn't fit well and also required some wood alteration - so i have decided not to install it - S&K was very easy on getting refund for this one.