5/16 torque converter bolts

The 5/16 pattern is 11+", and the holes are .337, for a .312 bolt.
The 7/16 pattern is 10", and the holes are .450 for a .437 bolt.
I would not use the 3/8 bolts you have , for two reasons . They are coarse thread, fine thread holds torque better and is stronger, and the heads on your bolts are thicker than normal converter bolts, and may hit the back of the block.
If your converter body is small enough that you can drill through and tap, have at it. If you will hit the converter body if you drill too deep.... I would probably get the best quality big head grade eight 5/16 converter bolts I could find, read ARP, some blue locktite, and fly it.
I was a machinist, I would have drilled and tap for a 7/16 fine thread like the factory did. That would be my preferred fix.