Will an old O ring dipstick tube work with a top hat style seal?
Should the larger diameter ring on the tube almost touch the case when the tube is bolted to the block?

No, and yes.

Those used to be easy to buy from GM, I think I bought an Allstar maybe to replace my old mangled tube and gauge, since I needed to update my gauge to the locking style and I ditched the CSI one piece shield.
The new one fits exactly as it should, with the top hat seal.

Thanks Goob, The lousy fitment of this tube is what's been causing my trans to push atf out of the vent. I didn't know the tube wasn't in as far as it should've been so I was over filling even when I would the fluid to a little under the add line. I never looked at the tube to case relationship be cause I thought the trans bolt to the block located the tube. It's an OEM tube with a stout bracket to locate the bolt hole. I've used this tube since the early 80's, but this is a different case. Sharp as a marble I am!!

Moroso makes a nice TH400 dipstick tube with screw-on cap/dipstick. Comes with a seal and does not leak.

Thanks Mike, if my repair doesn't work out, I'll check the Moroso set-up. I pulled the tube out and made the hole in the bracket into a slot. Put it all the way in and bolted it up. It hasn't leaked in the past, but it would push fluid out the vent tube. I'm sure I was over filling it because the tube was 1/2" from all the way in.

I’ve had to take a screwdriver or punch we’re bolt Tab is welded to stick and hammer them down on many Orem tubes to get them to locate correctly in case that bolt tab gets bent quite easily

Hmmm, you should never push fluid out the vent.

Are you running the deep GM truck pan or an aftermarket unit?

I just run the old genuine GM truck stuff, and have never lost a drop of fluid from anywhere.

I'm running the same aftermarket pan that I've run since 2006. I never pushed fluid out the vent tube until I bought this case, which was 2016ish. I think the only reason it pushed fluid out was that I was over filling it and that's because the tube sat up 1/2". I made 4 passes Sunday and I don't see any evidence of fluid in the vent tube I have going to a can on the firewall. I'm gonna route the tube to a clear Gatorade bottle that I mount to the trans pan. This will tell me if my tube modification worked or not.