replacement fuse block

After-market gages draw minimal current. Unless you have real loads, I would just use existing circuits. Many of the fuse outputs on your existing box have spade terminals. You can get "piggy-back" spades to add-on. Indeed, the factory did that (should have some). You can also get at constant 12 V from the cigarette lighter and glove-box. Some cars had mini-bullet splitters for that.

One thing to consider is to power the ACC circuit via a relay, actuated off the key switch output. I did that in my cars. May not be necessary but seemed prudent since I was bench fixing the whole dash harness anyway.