The later torque converter snout should be a tad smaller than the 1.810" diameter used for the later crank register hole. So just measure that TC snout diameter when you get it out. The '64 crank register hole and TC snout diameters will be considerably smaller. As said, late '67 was the changeover time, so it can be either on your particular '67; it just depends on when it was built, so you'll have to measure the snout diameter.
If you have the larger, later TC snout diameter, then you'll have to change the TC. That seems easier to me than modifying the '64 crank for a larger register hole.
As for the TC bolts, you can access them with the starter out on the /6. Use a deep well socket, put it on a TC bolt head through the starter hole, and let the crank rotate until the socket fetches up against the block casting; then you can put a lot more torque on the bolts with the socket itself holding the crank from rotating.