I have what I think is a Weatherby MKV Euromark. The action is 243 Winchester 6 lug LW action (the mounts are packed out at the front on standard Remmy 700s). The barrel is a #1 profile.
I have had conflicting information on it being and Euromark, Accumark, Lightweight and an Ultralght.
I need a replacement stock and have looked at a McMillan and they have told me it is a lightweight, but I do not want to order one that will not fit.
Is a Euromark the same as an Ultralight but in a wood stock?

I don't think it is. The Euromark and all the other "marks" I think are based on Weatherby's 9-lug Mark V action. If yours has 6-lugs, then it will be the smaller action that was used for the Varmintmaster rifles and Ultralights a few years ago. A stock fitting the Mark V action isn't going to fit the Varmintmaster type action.

Curiously enough, the new Ultralightweight actions Weatherby is making are the 9-lug Mark V actions, but are smaller, a stocking fitting a regular Mark V won't work with one of those actions either.

The ultra;ightweights in stadard cal. use the six lugs, magnums use the nine lugs.