I dug up an HEI (not Tom Langdon's but another) I had modified from another Chevy 6 to fit the 235. It was removed running and cleaned up but the floating mount was not altered. You can see it and the measurements below. Total length from flange to tip...4 7/8", bottom of flange to bottom of toothed part of gear...2 3/4" and bottom of flange to very bottom of driven gear...3 3/16".
There might be, but I don't know about that. I remember pre-54 had a forged camshaft and used a different gear. the gear on the camshaft was a bit more narrow as I recall. Then in 1954 I think they went to a wider gear and that's what I'm assuming you have. The width of the gear on mine (a 1959) is about 5/8" as I recall.
Well, they only sell one distributor. So logic says it's not them. The only option is a steel gear for pre 1954. Did you buy the distributor yourself? Has anyone replaced the oil pump? There online pic shows a gasket/spacer and an Oring. Here are my guesses: 1. You are NOT in the slot 2. Someone has been playing with the Langdon distributor 3. It's a home made "Langdon" copy 4. It's all together the wrong Dizzy 5. Most of these guesses will be wrong if you yourself actually ordered it from Langdon. Seems like if you did you would have called or emailed them. 6. I see your hobby is "gears" hmmmmm, did you play with this dizzy?
Watch out for careful drivers!!! I'm away on an ego trip. Will be back on Feb 30. I'm not an Auto Mechanic, but I play one on TV. I charge $0.02 for every opinion and I take Paypal. Plan B is always better than plan A, by definition. You can't teach a new dog old tricks.
Two other thoughts: the width of the driven gear in both the stock distributor and the HEI distributor is 5/8". Is yours for some reason different? I can't imagine it would be, but probably need to know. Also are you certain the bottom of the gear is hitting the internal flange? Can you see down into the oil pump connection? Is there any way something...anything...could have dropped into that slot? Maybe if you could use a bamboo skewer to measure from the bottom of that slot to the top of the block where the distributor flange will sit?
It is a Langdon stovebolt mini HEI distributor purchased recently from Jim Carter. I am sure it has not been modified, but it appeared to be an open box. It came with an 1/8" thick o-ring, but did not come with a spacer or gasket.
Oh, I thought you bought it from Tom directly. That would have helped in this case, but you could call Tom and ask him, I suppose. I think it should had a flat round gasket, too. But that gasket is only about 1/16" thick or less. Here is a link to Tom's website:
I can tell from the dirt line that my stock dist had a 1/8" gap between the block and the shoulder on the dist, but it didn't matter because it had an internal o-ring and the retaining bolt did not push the dist down. It just kept it from rotating.
l'll check with Langdon tomorrow about this gap I have.