What a mess, my sympathies!
I'd have thought the cam locks would be hardened. Hardened steel on hardened steel makes an excellent bearing surface (look at all the 100 year old watch lathes that still are perfect) but soft steel on soft steel will gall, which is also called cold welding where there is contact. If this is what has happened, penetrating oil isn't going to fix it, although lubrication will make it easier if you can break the contact/cold welds (if that is even what has happened....but I'd guess there's a good chance of that being the problem, seeing how soft that cam is)
This stuff was just discussed on another forum
Apparently it works, and is more effective than the old dodge on using valve lapping paste. Speculation was it has jagged particles of carbide in it so really bites into things.
Might worth a try. I'd be thinking a close fitting key out of something tough, say a HT chrome moly and this stuff.
The other thing on disassembly is that sometimes you can avoid breaking things or brinelling bearings by using lots of little taps vs a massive WHACK. Maybe an air gun? The high volume of impacts of an air wrench for example might be the thing.
Making a spindle is a big job. I made a few but never that large, its exacting work. Just getting a bore straight, that long and of that diameter presents challenges. You'll need more HT chrome moly lol. If it get so bad you've damaged the spindle, I'd say new bearings are in order as well. Ugh. Hopefully it doesn't get to that but if it does, is it worth it?
..........................................
Idea two.....get the spindle out of the lathe an on a mill. Start pecking away at the jammed up cam with a small carbide endmill until things can be pried apart