Tailgate, You can use either standard or long actions in the 700 Rem action to build a .308 Win. The only reason I can think of for using the long action would be, converting to a 300 Mag at a later time which would require opening the boltface, feedrails and rechambering(the Army's M24 SWS is built on the long action for this reason)If you go this way(which I don't recommend)you will need a long action with the .473 boltface 25-06, 30-06, 270Win, 35Whelen etc. If you use the short action(which I would recommend) It will have the .473 boltface 243Win, 7mm-08, 308Win., .358Win, 22-250 etc. If you plan on getting rid of the aluminum and putting on new bottommetal it really doesn,t matter if you start with an ADL or a BDL. Moving on to the Mauser,s I had a 300Win Mag rifle built on a Mark 10 it is my favorite rifle I used a McMillan stock and a Douglas Airguaged barrel I shoot .5 M.O.A at 300 yards with it and I,m sure it shoots much better but I wouldn't do it again for two reasons the trigger is a pain in the ass and you are somewhat limited as to stocks inletted for Mauser's. I think you save youself a lot of trouble by starting with a Rem or Win receiver when you build.
Hope this helps, Rabon...