You are making something that is very simple into something difficult. For one, you do NOT need to use a 4 port BG for a nitrous regulator. That's a waste, plus they are not repeatable at low flow and pressure.

You asked about a log, you don't NEED a log. That 4 port has a rear port that is flow through, meaning it sees pump pressure. It's probably a 10 or 12 o-ring thread. So you buy an adapter that is 10 or 12 o-ring on one side and 8an on the other and screw it into back of reg. Now you have an 8an port. Then get a bent 90* female to female 8an 90* fitting and screw it on with the bend pointing up. Put a 3/8 pipe to 8an adapter in the bottom of a 803 Holley reg and screw that to open end of 90* fitting. Now the nitrous reg is mounted directly to carb reg, is seeing pump pressure and is your dead head nitrous reg. It's mounted, ready to go and you need no log. Most run 6an to fuel solenoids but 4an is fine. I would run a 12 from cell to pump and 10 to front and into carb reg

That motor is liable to be a turd with low compression and a small cam. Not sure why he did that either. Also if the 500 came out, the 540 would go right in, not not sure what the couldn't "shoehorn" that in there comment means. This car has taken about 6 different directions since he bought and it sounds like he is still not sure what he wants to do.

First he wanted a Pro-Charger motor with blow through and bought a setup. Then he wanted EFI. Got mad at me, because I refused to wire EFI into his 40 year old stock wiring harness and said I would only do it with a total car rewire. Then a 540 with Pro-Charger.......seems a Vortech was in the mix and now back to a nitrous motor, which it was when he bought it. So I can't keep up...........LOL!!!!