I had a real booger of a time getting one out that was rusted on a 78. First there was so much rust that it wouldn't let the cyl. slide all the way off so I ended up cutting the top thread off, used some heat and vicegrips and twisted it off right in the middle, more heat and oil only to twist it off at the base. center drilled it, more heat and oil. It started coming out then broke my Snap-On easy out.
Now I'm no animal. I took my time, spent a couple of hours and a few days letting things soak in. tried it again with heat and oil with another easy out and broke that one.
So off to the machine shop I went with the top half and a spare stud. made a point to show them the counter sunk hole the stud was to go in and of course they missed it the first time so I had to come back the next day to pick it up.
I have like seven spare engines and two cases in the shop. Any other time I would have scrapped it and picked another one but this one (aside from having one rusty stud) was near new, Std bore with less than 0.002 wear. I could still see the hash marks in the cyl.The rod and main bearings looked like new as did the trans and clutch thus making it worth the the stud trouble.