Originally I was just going to refurbish the heads on my '66 have them milled a hair, and then install with new gaskets (since head gasket was leaking, but no loss of compression).
However,
I took the heads off, I noticed a couple of my cylinders were wet, and showed LOts of carbon buildup (no coke, just black carbon hardened soot).

My rings might be a tad loose as well (just allowing blow-by) Since the head is already off, is now a good time for a quick rebuild? and if I do rebuild, what new parts are a must and what parts can be re-used provided the wear is nominal?

Caesar

Also what tools to check wear and clearance? feeler gauges i have, but what else.?

How big is the ring ridge at the top of the cylinder? Is there a double ridge in any of the bores?
Measure the bore wear to decide if you can get away with a basic re-ring job instead of reboring the cylinders.
DD

The least I've ever done, while having the engine out and apart, was to hone the cylinders, put in new rings, give it fresh bearings, and have a valve job done. That was on a Chevrolet 230 inline six. It had just started to smoke a bit. That little bit of work let it run happily several more years, before I sold it for a profit.

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"When you find a big kettle of crazy, it's best not to stir it." - Pointy-haired Boss

1964 Valiant V200, 225/Pushbutton 904
BBD, CAI, HEI, LBP, AC, AM/FM/USB, EIEIO

If you are checking the cylinders' bore diameters, make sure you check several different directions to determine if they have worn in an oblong (oval) shape.

Jerry

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There's a difference between ignorance and stupidity.
Ignorance is not knowing any better.
Stupidity is knowing, yet doing it anyway.