[350TacoZilla]

What about cutting the top off each one and switching the bottoms around, tack them while in the truck then pull them out and fully weld and add a gusset. That way you have the tops that fit frame nice and bottoms contact the crossmember, you could also negate the need for the spacers on frame that way.

If all else you are using the older style motor mounts like that where the rubber is bolted to engine you can just use tube "stands" off the frame for the motor mount bolt to bolt through.

Hope you dont mind me hacking up your pic.