On my M 51, the hole spacing is the same on the front and rear of the action.

A one piece base does not fit, as the rear hole is between the two rear holes.

If I use a two piece base, I can't find one with wide enough holes.

Any ideas or am I forced to drill a new hole in the rear?

Did you try Model 70 bases?
I think this is correct.

I will go look at mine later today and post what it uses!

I have luepold 2 piece reverse front, bases for FN/ jc higgins mauser on mine.

The post-1955 actions have the same spacing front and rear, and the regular FN bases don't fit them. Did you try the Leupold #49989 one-piece base?

Terry,

If you have the action with the hole spacing at .875 both front and rear, no bases are currently available... You have to go fish in parts boxes for an old set of early Leupolds? with an arrow marking the direction of the mount (the only marking on the bases). I came up with a set- Talley rings fit these bases well and as an added bonus mount the scope considerably lower than Talley bases...

Or, have a custom set whipped up by one of the machining wizards on this site...

Conetrol might have bases, but their mounts are expensive as all get out.