I can't answer those as I do not have a 239 block to look at. and I don't know how the dipstick tube fastens on a 'Bird.
If it is simply that the tube does not go as deep in the 239 block, then the diameter's are not different. What you could be experiencing is a tolerance stack up. A 1/2" drill bit is not going to be dead on the money .500". For example It might be .051" or .499", that would be +- .001". No idea if those are real world numbers for the manufacturing tolerance of a drill bit, only an example. If the 239 was drilled with .499" and the 292 with .501", then it is possible the 239 might be more difficult to install and seem to stop sooner.
It is only a counterbore for the rear sump location. I verified on some spare blocks. So no sleeve. DO NOT try to get it out.
Lawrenceville, GA