Hi all. I've recently had a 1275cc engine built using an 1100s block.
My engine builder completed the assembly of the engine. He said he had some difficulties getting the distributor to fit properly and said he suspects that the distributor we were given is an A+ instead of for the A Series.
I tried to install it this afternoon and I found that it went it with no dramas. I've never removed/replaced a mini distributor so I want some advice please. I've taken some pics tonight showing how I was able to install it. Can you please let me know if it is likely to be an A Series or A Plus distributor:
(Apologies if this sounds like a double entendre)...
Initially the shaft slips in smoothly and easily with no play - it feels like the perfect fit. It doesn't go all the way in, until I rotate the rotor gently. Then it feels like the drive slot lines up and the shaft is then allowed to drop in further. Once this was done the distributor sits with the flange butted up against the block/gasket like this:

You will note that while in this position, the distributor body can rotate:
Before rotation:

Rotated a little to demonstrate the movement:

]
But when I try to move the rotor, it does not revolve:

The engine is at TDC for 1, and it has spark plugs in it, so preferably I wouldn't turn the crank to check if the rotor on the distributor turns. But I can test that if it helps.
I wanted to see what it was about the distributor that made it not fit (if the shaft was too long/too short, too wide/narrow or it the slot was too thick/narrow). But given the dummy install above, I'm included to think that perhaps the engine builder just coincidentally/accidentally didn't manage to get it lined up properly. But perhaps there is something I am missing and the distributor is an A+? The engine builder is very well respected and has done a lot of excellent work.
What do you think?