Big Block Distributor won't seat..

[72BlueGMC]

heres the deal, I have 454 out of a 85 Suburban I stroked and I am installing in my 72 C10...

I am looking for some advice, I have a 454 out of a 85 suburban that I am turned into a 489 (or I am trying). At this point I am trying to use the stock distributor because I have sunk a lot of money in everything else. During reassemble I have tired to drop in the stock distributor several times but I can't get the last inch to drop.

I feel it engage with the cam it gets very sold at that point and I have tried to turn it to line up with the oil pump shaft MANY times.

What am I doing wrong, surley this isn't a first.....