Front/rear balance after front disc swap

If you are going to use the drum/drum MC, then you need to remove the residual valve in the front brake line port out of the MC.

Also, be aware that the drum-drum MC has a much smaller front reservoir fluid capacity than the ones made for the 73-76 disc/drum setups or for the Kelsey-Hayes disc system. So as the pads wear down, you will have to add fluid to the MC, and then remove the excess as you push the pistons back when you renew front pads. The correct disc/drum MC avoids this issue.

Yes, you can do as you suggest as long as you have the split for the front calipers.