[Rory428]

Be aware that if you do any grinding or welding on a SFI certifed bellhousing, you have effectively rendered that SFI approval void. If you don`t race the car, not a big deal, if you do race, it could be.
On my cars, I use the offset dowel pins to get the housing "dialed in". To prevent the dowel pins from moving out of position, I hold them in position with small Allen headed set screws that thread into holes that I drilled and tapped into the block near the dowels. This way they can`t move if you need to remove the housing at some point. Also, if you were to do the welded washer deal, it would be good on that particular engine block, but may well not be within spec if a different block is used later on.