I suppose I'm not 100% sure what you mean by 'conversion motor mounts' But I have just converted/swapped the crappy GM 4.3 SyTy mounts for JTR heavy duty 2.8 mounts and so far am very happy with the fit and engine position. http://www.jagsthatrun.com/Pages/Parts_S10-43-2wdRepacementMounts.html
The hardest part was removing the original mounts first. http://www.syty.net/forums/showthread.php?t=91854
They (JTR) also do V8 SBC and LS conversion mounts too, if thats what you were meaning.
Hope that offers some help.