I think if you go solid the whole way you'll be fine. I'm using solid motor mounts, engine plates, atlas adapter mount and a solid support ring. I suppose some of it will also depend on limiting chassis flex.
I choose to go poly because I don't want my drivetrain trying to limit flex in chassis. I say go poly and add extra mounts. Engine, midplate, transmission, and t case.
Really depends on how aggressive you are or plan on being with your buggy. I would recommend solid mount if you are planning on aggressive driving. Load - no load - shock load (high RPMs climbing a steep hill with the wheels coming off the ground at times) the sock load is another situation you could twist your drivetrain enough to crack a housing. I would not recommend it if your chassis isn't braced against flexing. Like X bracing.
Way back in the 70's when I built VWs, it was wise to go with solid mount and case straps with high performance engines. I've always used it since. My buggy today has an ls 6.0 with some tweaking to a th400/203/205 all solid mounted and really no vibrations at all.