Which Manifold spacers would I require to fit the MACE/VCM OTR is it the 6.35mm or am I able to go thicker on my 2011 VE SV6 LLT Engineprovided the radiator mounts have changed on the LFX.

When installing a MACE/VCM OTR manifold spacers are required. Either the 6.35 or 12mm manifold insulators would work well on an LLT engine, or if you had an LF1/LFW/LFX engine you could squeeze a 25mm insulator with a bit of work.