Nearly every engine on Earth uses two bolts per port.  Some, like the GMs, Mopars, and AMCs with siamesed center ports, use two for those ports.  Two works just fine.

The active ingredient in Stabil is butylated hydroxytoluene (BHT).  BHT is a petrochemical preservative and is also used in the food industry as a preservative and by the health supplements markets as a dietary supplement.  You can buy crystalized BHT fairly cheap.  One teaspoon treats 10 gallons of gasoline.  Here's a site for it:  https://www.accessoryz.com/us/products/butylated-hydroxytoluene-c15h24o-99-usp-grade-crystals-6-oz-in-a-bottle-usa-90a9caf5e3d937cef8abf6c292128aa11bd80b89?v_id=variant_01KWPW86J2H99PA1N8M92VX1KH  You can find it on Amazon but you have to make sure you're looking at crystalized product, not capsules.  Here's a link:  https://www.amazon.com/Butylated-Hydroxytoluene-C15H24O-Crystals-Space-Saver/dp/B014H17CLW/ref=sr_1_4?crid=3OWHRCMV5ES1U&dib=eyJ2IjoiMSJ9.chM832AjHoWZUuXI8sBVvSvcxZRuUudd3uNWlAeWD51S6e5bOyVuN7lVh4P6L_r2QeSe2wUS-TiG-B_GBhiDo_Mlrpe2cu0WoNePtCpas_FmqNzu0EF7mZuPKBxGm3HoKxQEpbObjlLTDxLK0TwdackPZKbAUnwMeL1zi0K-L_LKR-ihC-8Kh5M9-EzrWeYG.KPehatPwYTFcWLOS-n7C_zoWucixECuWNC7GRFYa5VY&dib_tag=se&keywords=butylated+hydroxytoluene+crystals&qid=1784471235&sprefix=butylated+hydroxytoluene+crystals%2Caps%2C161&sr=8-4

That is correct.  Crites did make a replacement z bar that was a solid piece.  I don't know if that's what Autokrafters is selling.  You can still buy the nylon bushings.

Most carburetion problems are actually in the ignition.

If the wires from your pickup are not twisted together, try twisting them up.  Twisting the wires together along their full length allows the wires to reject EMI through the principle of common mode rejection where the EMI affects both wires equally and cancels out.

You're too far down the rabbit hole now, but what you should done is a diagnostics before a teardown.  In this case, it would mean pressurizing the cooling system to see if it holds pressure.  Then a compression test to make sure the cylinders are doing good.  Brent has a lot of experience here and right now, you have to go with the intake gaskets as the culprit.  You could also be dealing with a casting issue.  You might be in the position of putting things back together and taking due diligence to make sure the intake isn't leaking (this time), then pressure testing to make sure it holds pressure.

You can't run anything from the coil + other than the coil.  If you want to have the pump turn on only when the engine is running, use a relay with the trigger coming from the alternator stator terminal.

Oddly enough, there's a company called Ohio Crankshaft (https://ohiocrank.com/) that is one of the best known crank shops.  Not too far from you.