This is the gap where the block meets the dist base. Is this normal? The dist wont go down any further. The gap is about 2mm. The pic angle is right where the hold down would go. I dont remember if this gap was there when I took it apart.
Just put a new distributor in my car and had the same thing. Basically it just needs a little help going the rest of the way. Push down on it harder and it will slide into place.
I solved it. The retainer ring on the replacement shaft was positioned incorrectly out of the box. I moved it to the same position as the retainer on my original shaft. Everything easily comes together flush and the the shaft still has room to move up and down like it should.
Man, I solved it first then read your post a minute later. Now, tapping down on the dist might get it to go down but those retainers are designed to slide on one way. They're not meant to be forced back in the other direction. Even then it should have additional play so the shaft can float up and down a tad. So knocking down on the dist would get it together but likely would not leave the shaft with room to float.
There's no doubt you were on to it though. All good now....
This one of those things that often gets over looked when assembling an engine. I always fit the distributor to the block and check the retainer placement before the oil pan goes back on. Part of the learning process for some people. I over looked it on my first build, but was lucky enough to not have an issue.