Some of the new actions I have seen on the mod 70's actually use the FN action. Its spaced differantly than the standard Win 70 long action. Had this problem a while back with a Mod 70 in .308 HB Not sure exactly what model it was but the rail from the FN fit.
Here is a link to what the action actually was.
FN A1 SPR
Check it out and see if it will work. Not sure that is the exact model but the long action in that model is what rail it actually took.