Distributor install woes...

[nikwho]

Hello all,
I'd like to say that I have installed MANY distributors, into many SBC, BBC, SBF, BBF, mopar, Pontiac and Olds engines! I've also never had to ask for help. So, old 350 came out of my '59 Apache. New 383 is going in! I have engine at TDC of compression stroke and oil pump shaft slot oriented towards front/rear of vehicle. Absolutely cannot get it to drop into place! Also, BEFORE the camshaft gears engage, I can feel the oil pump drive shaft engage! I can pull the distributor up a little and only get it to re-engage rotated 180°!

So, now I start playing with my oil pump priming tool. I seat it easily into the old block and have about 5/16" of shaft "reveal" above the anodized piece of my primer tool. When placed into my new 383 block, my oil pump primer tool has approximately 1" of reveal! I can feel that the oil pump drive shaft is seated in the tool on both engines.

So, what might be creating this discrepancy of approximately 11/16"? Does that happen to correlate to the difference in length between say, a small block oil pump drive shaft and a big block oil pump drive shaft? I'm thinking that this figure of approximately 11/16" (actually closer to about 0.710") For clarity, the oil pump shaft is engaging before the distributor gears are meshing with the camshaft dizzy gears, preventing the distributor from dropping in all the way!

I'm SUPER bummed, as I am afraid that regardless of the cause, the engine is going to likely have to come back out and the oil pan be dropped! This sucks because I was about to install the distributor with the engine still on the stand and thought "nah! I'll just do it once, while the engine is in the truck! I never install engines with the distributor installed, to protect the distributor and firewall.

Thoughts?

Thanks,
Nik