I suggest a cheaper and safer guillotine is a simple air cylinder powered by
a portable air tank. I bought a new 2" bore Bimba cylinder on eBay for $15
and an air tank with pressure gauge from Harbor Freight for $25. A
"pop-open" push-button air valve and some air hose completes the system.

A 2" cylinder produces exactly 3.1316 pounds-force for every PSI. The tank
holds over 100 PSI so the cylinder can drive a chisel blade with at least 313
Lbs-F which WILL cut a rope. Checking the gauge on the tank assures you have
air pressure. If necessary, refill with any shop air compressor. Unlike a
steel spring, compressed air doesn't rust or lose strength with age.

Why is it safer? You can de-energize by just removing the air hose to the
guillotine so there's no chance of losing a finger. Spring powered
guillotines resemble bear traps and have to be relaxed VERY CAREFULLY to work
on them.

I don't think we had to worry about the spring losing strength. It took
around 500 lbs to compress it IIRC so it had some margin. Valve springs
on cars sit compressed for long periods without losing strength. Might
get rusty, but the winch was only outside when being used. No argument
about the bear trap. We did not put our fingers anywhere near that thing.
We "relaxed" ours by firing it. Not a gentle process, but worth it in
entertainment value! We never fired it in anger, not sure about
subsequent users.

I drove about 2000 launches with that winch and I miss it!