Hi Ken, my Carb coach pager finally went off, so here I am...
First off, I Thonk those x-shaped slots on the bottom that connect all 4 barrels to the center MIGHT be for the Power Valve. In fact, I'm almost certain of that. Best way to know for sure, is pull the primary fuel bowl and metering block off (off the engine). For your sake I hope Holley is using non-stick gaskets now!! Once the Primary side is off, you can verify, you will see a cavity on the center body that matches the location of the Power valve in the metering block. I think that hole in the base at the center of those X slots is the manifold vacuum signal port leading to the Power Valve. Do Not mess with those!.Don't fill in those slots.
I think that Holley started adding in Power Valve backfire protection to their carbs years ago. Is this one brand new? I've installed the power valve anti-backfire kit a couple times, I believe it is just a check valve that goes into the port in the center of those x slots. If yours doesn't have the anti-backfire kit already installed, you Want to get it! Holley power valves are a diaphragm type and very vulnerable to engine backfires. A blown power valve sucks, instant over-enrichment that persists 'till you replace the bugger Power Valve. That cheap power valve anti-backfire kit can save a bunch of grief, if the carb wasn't already equipped.!
As far as all the vacuum stuff goes- none of those should cause any trouble to keep hooked to full time Manifold Vacuum. (Except the PCV vacuum of course!) Distributor, power brakes, vac. gauge, or anything else are all dead-end users of man. vacuum. As long as they don't leak, well there's no vacuum leak, right? I cant exactly say as to your vacuum nipple access on the intake manifold. Would a carb. spacer help? IF there's underhood room for the increase in air cleaner height, that might give the access to the manifold vac. nipple you speak of. Personally I like the 4-hole type carb. spacers only. I avoid those open center ones, those are for racing. IT's Winter now, but come Summer you might face carb heat soak issues, vapor lock, excess fuel vapor venting underhood, etc. etc. Awhile back I did some mods on a guy's Ford 460 engine w/ a Holley carb similar to yours. Heat was his issue, I solved it w/ the right spacer setup and insulated his fuel line underhood.
Back to the vacuum hookups- if your4160 has the same vacuum ports and nipples as the one in the pic here- well i see the power brake port on the rear, and the PCV and smaller manifold vac. port up front. I know I could provide manifold vac. to everything you have mentioned, with those 3 ports.probably even if the carb sits flush on the intake man w/ just a thin gasket under it.
Make sure that the carb.is adjusted with enough idle RPM set to position the throttle plates somewhat cracked open, BEFORE ya Groove it, Ken. You might even want to set your curb hot idle speed , then when it's off the engine see if you can turn the idle speed screw in some more (record how much ya turn it here if ya do). Assuming there is adequate room under the cracked-open throttle plates to fit your planned Groove. Not much throttle bore left under those primary butterfly plates. It's better to place the Groove a bit downstream from normal idle plate position, than to back out the speed screw in order to "make more room". Obvious reason being- Putting the Groove too high up in the bore, and it will be idlling "in the Groove". And ya don't want that, could give erratic idle, difficult to control idle RPM's. Ya want to idle "out of the Groove" and transition into it OFF idle!
Once you Groove it, you might need to re-tune it some. But that on-board Air-fuel meter gauge will be big help there. I will also mention another carb. tuning aid, Color Tune. That is a special glass clear porcelain spark plug that allows you to see the flame color at idle. But you can't drive with those, use just in the driveway.
I hope this helps, Ken, ask again if you need to.
Tracy G
