There are no dumb questions.
Exactly, that's why we HAVE questions.
The answer to both of your questions is, "It depends."
In fact the answer to most sailing questions is, "It depends."
Can you go to the top of the mast on a Cat 27? How big are you, how strong are the halyards, how strong is your winchman? Yes, it's possible for the right person... but check your equipment carefully and have a safety line. The only thing worse than having to go up the mast is only going most of the way up the mast.
I went up the mast of my quarter tonner - a tender 4300 Lb 26 footer - several times. The mast was 33' and I weighed 220 - do the math - that's over 7000
Ft/Lbs of potential torque. A very hot car might have 400 - 500 Ft/Lbs available.
As long as the boat stays vertical there is no torque effect but get a little bit of heel on and you very quickly get a gut feel for the term "tender".
I wouldn't climb the mast on any boat that displaced less than a couple of tons and more is better. A Cat 27 is over 3 tons, so no problem if things are in shape.
Get a good bosun's chair, rig a safety line (a spare halyard), I like to have a waist line around the mast as well, to prevent swinging out and don't do it on dry land - you can develop enough torque to knock a boat off its stands if anything goes wrong.