If you measure the oil way in end of block, I think it's just under 3/16"?
Bolt block to head, run 3/16" extra long drill through from bottom to make sure everything is lined up, counter bore for dowel same as the ones on alternator cover, half in head, half in block then use end mill to make recess for "o' ring
The dowels on rear studs will keep everything in correct position.
The amount of stuff you've learned doing the motor so far, I doubt you'll have any issues doing this, it really is as simple as it sounds
It doesn't have to be super high precision, the dowel is to support the 'O' ring rather than locate block/head