Thanks for the replys !� Dumb ? But how do I support the trans/ transfer case if I remove the crossmember 
?? Or should I just loosen the crossmember bolts & somehow raise the transmission / trans case & install the new rubber mounts� :-/
Either use a strap around the transmission thru the floor hole, (take the shifter cover off first) hooked to something overhead like a beam in your shop, or use a jack underneath the bellhousing area. If you keep the engine mounts hooked up while you change the tranny mounts it shouldn't rotate due to the offset center of gravity. Change the engine mounts the same way, and I guess it would be smarter to change them first. Use an engine crane or overhead hoist with a strap around the engine or a lifting chain, or a wooden block on a floor jack under the oil pan. Put a little tension on the engine, then remove the attaching hardware on one side, lift it up, replace the mount, drop it down and bolt it in, then do the other side.
You'll find a long tapered punch helpful in lining up holes to put the bolts back through.