Bulkhead Delete

I did on my 67 but its aftermarket harness. It's fairly easy if you have basic metal tools. Make a steel plate the same footprint as the bulkhead connector. If done right it will snap right into place instead of the connector using the same gasket and retainer clips. Punch a hole for a big grommet. The trick is likely getting a grommet. Some of the aftermarket wiring outfits likely sell them separately.

You will want a large grommet with lots of stretch for adding "whatever," tach, etc

There is no connector that you cannot fish through the hole, although of course you'll have to pull the ENTIRE harness if you remove it

Another way you could go is to pull (likely the underdash harness" loose to make slack, and feed ti partway out into the bay to work. Then document all connector wiring, and just remove all terminals from the original connector, and put it all together "empty." Then reassemble, and drill clear through each one and feed each wire through then splice on one side or t'other heat shrink, but splice, whatever. You might want to use sealer in each cavity when all done