0ne of 'em ISN'T a 2005 and/or a 2.5.... same liftin' eye fits all tha V6 Mercs!!!
flat/square heads are O-ring style heads which would be right for 2005... roundish or "dome" type what sounds like your describing are pre 2000 gasket type motors....I am referring ta U.S. motors..justa 'bout all 2.0, 2.4, 2.5 power heads will interchange but with a few changes that need ta be made... depends on early or late model years.. tha main difference would be tha exhaust adapter plates...but if they are both are 2.5's and/or "fat blocks" year will not make any difference.......
we need pictures!!!