dr71749
Just had one fabricted for BV-20 to fit on bedding block LR 338 Lapua Ack Imp HG. Any decent gunsmith with milling machine can mill a one piece base for unertl scopes with correct dovetail and tapered to fit Rem rcvr. Key is to go 7.25" spacing for true 1/4 MOA clicks where unertl bases will go. Good cost estimate is $100-150, depending on smith.
Depending on actual mounts you have, will have to mill small recess for detents on mount to go into to ensure stays in place and ability to take it off and return to correct place, otherwise it will not lock in place and if you take off will not get correct spacig when you put back on.
Is your mounts 1/4 or 1/2 minute clicks? Both are out there, you will probably want 1/4 minute.
BH