Guys there was a tread on this last year. First Get Allen head bolts to bolt to the block. Next drill or grind out all the bolt hole on the bell housing befor mounting to the block. Mine was .032 out when I started. Your pins are long enought that you can weld nuts to the bellhousing after you center it. Clean the center hole with a wire brush, NO GRINDER. Put 2 bolts on by the pins and do the measurements. You want numbers at 3,6,9 and 12 oclock. I used a deadblow hammer and banged the bell housing to center. This takes time, 2 hours when in the car. final for my car was .002 when done. After centered add all bolts and recheck measurement. If OK get to nuts and grind out threads until they just fit on the dowels. Weld them top and bottom to bellhousing. Let cool and recheck numbers. You should be right on the money. I have not tryed to mount my bellhousing to another FE motor and check for center. Your bellhousing may only work on this block when done. When WELDING UNHOOK BATTERY TO PROTECT ELECTRONIC IN CAR.
Good luck, check the measurements twice, the magnetic base may move sometimes.
Rick Lake