Actually, the issue M670 stock will accept the Model 70 TG w/floorplate, magazine liner, etc.
IIRC, the follower & spring you now have should fit/work OK.
Just run a small drill(bit) down/out through all four corners of the blind magazine well, then cut out between the holes & clean up to get straight/tapering lines that match the M70 bottom metal.
The bottom of the stock just ahead & behind the new magazine opening will also need to be inletted for the bottom metal.
(I've added the upgrade to both Win 670's and old Rem 700 ADL's, both using new factory parts from the respective Parts Dept's)