UCA bolts stuck rant

Common problem in the rust belt.
First, because they are rubber encapsulated, impact tools don't work because the rubber absorbs the impact.
Second, a reciprocating saw needs clearance for the saw blade to move back and forth. Not much room there.
Nowadays, I'd probably use a rotating cutter to cut them up.
It's been well over 25 years since I did my 69 but I remember working on them for several evenings as I didn't have as many tools back then. I finally gave up and carefully cut what was left with a cutting torch. Always the very last resort for me.
I was so happy when I finally got them out.