Depends upon "which" distributor is stuck! The cast iron Holley and delco units usually don't end up in this condition since both the materials are cast iron!
It's the aluminum distributors (Holley, prestolite, and in some cases lucas) that seem to grow to the block due to the reactive nature of aluminum, cast iron, grunge, and water over the years.
I was visiting a wholesale engine core supplier in the portland area just today and we talked about this! They have the same problem when stripping out IH sv and mv engines they purchase in bulk from around the country for breakdown into core parts!
The supplier has the advantage of the engine being on a pallet and the distributor is easily accessible. Turns out their methodology is the same as mine...plenty of pbblaster and patience! They do not want to risk damaging any core part off these engines since that is how they generate their income...and have been doing so for over seventy years! A destroyed Holley distributor has no value as a core if it is damaged even only cosmetically.
In extreme cases, what I do is douche the entire distributor base area with your penetrant weapon of choice, then using a very light hammer, start "tapping" around the lower portion of the distributor body, the vibrations from the tapping action aid in lubricant penetration. Do this several times.
The next step (if needed), is to strip any thing flammable back from the distributor area, and then use a heat gun (preferable) to really warm the boss of the block where the distributor penetrates with the idea of expanding the cast iron just a touch to allow the penetrant to work better. If a heat gun is not handy, then I use a oxy/acetylene rig with the smallest tip I have as a heat source. And playing the heat on the distributor body below the upper portion helps also.
The last resort...I rig a bearing separator on the distributor body, with a cross arm puller attachment and a slide hammer. Sometimes the distributor will then pop right out...sometimes you will whack on it until the distributor is destroyed...it'sa 50/50 chance so be willing to deal with the consequences!
You mentioned a technique for dealing with fords...I can remember using a "rolling head" prybar on those occasionally in the old days. I haven't tried that on an IH sv...but I think the Ford (at least the fe motors) have much more room for inserting the prybar than an IH sv.
