Help! installing distributor, won't drop in

[txriverrat]

Hey guys,
I bought one of the Skip White HEI distributors off eBay, got it in the mail today and went to drop it in, but it won't sit down all the way. It feels like it's all the way in, but there's still about 3/8" gap between it and the block. I tried moving the crank while my dad wiggled the dist, but it wouldn't drop. Please help! Do I need to keep rotating the engine till the dist. drops in the rest of the way? I was wary of doing that and throwing the timing way out of whack...I dunno what else to do though, not much experience with v8 engines, kind of learning as I go.


Thanks,
Cole

edit: truck is a 69 with a small block 350