I have close to 28 Champion RJ12YC made in the Mid-90s on my shelf and I currently have the 906s. However, I will be switching over to the Edelbrock's very soon here and I am reading threads on the longer plug slapping the piston and blowing apart the plug and causing damage.

I am noticing alot of people running NGK but how do I select the right plug for my engine. I am concerned because its switching into a different beast.

-From 906s to 84cc Eddy's
-Staying at 9.5:1
-Staying with Pro-Billet, MSD coil, and 6AL box
-Switching out from HP manifolds and going to
Shorty Hedmans
-Switching from a Single 750 Performer to a Dual
Quad (Dual 500s)

Is there a chart or something that someone can point me to? I think i will have to order the plugs and its gonna take a while to get here

Personally, I would feel a whole lot more confident by doing an actual measurement after a test fit than relying on any chart or book.
Too many wariables. Deck height, piston, gasket thickness....

I'm about the same compression as you and ran the RC12YC's with Stealth heads. I'm running Autolite 3924's now. The lower the comp, the hotter plug you need.

IIRC the only time you will run into a hitting problem is with a dommed piston that doesn't have a plug relief notch.

I'm running 12-1 CR with shaved eddy heads and the plugs don't hit

Clay on top of the piston will show you how much clearence you have.

My motor has flat tops sitting .010 in the hole, a felpro 1009 .039 thick head gasket and my Eddy heads were shaved .090 and my plugs don't hit.

In other words, unless you've gone more extreme than we did, my bet is you'll be fine.

The Mancini store has a series of plug recommendations based on head type and compression. I used one of their recommendations for a 10.2:1 Ed headed stroker and it worked out fine.

The NKG's I used are available with both projected tip and recessed tip. My combo has a dish piston so no worries with the projected tip.

With a flat top piston, measuring before choosing the projected tip sounds like a good idea. The recessed version would be a safe choice but could leave a tiny bit of power and economy on the table.