ez, first thing the dealer is going to hit you with on those valve guides is that mercedes dont offer a standard guide for the 3.5 head,he will want to machine the head so that oversize guides will fit. better ask first.
the standard size that trw has i believe are about 10 bucks a guide and fit perfect,no reason to do any machine work.i get time i will look up because i used a set last week on a 3.5(91sdl)
dont have a clue to the total cost but parts are less than 150.00
larry perkins