S&P's work well but the thickness can give you some problems trying to get the bolts to line up with the mounts. If you have access to a cutoff wheel, some 1/4" to 3/8" mild steel plate and a drill I can send you thed dimensions to make your own.

I bet these would work great for the price and they look like the same positioning as mine.

CAR SHOP LS1GM LS1 LS6 CONVERSION MOTOR MOUNTS ADAPTER PLATES $39.95 BUY ONLINE