Before U even pull the damper -
Check Top Dead Center (TDC) and see if it matches what the damper/pointer says.
Then - get the stuff to degree a cam (dial indicator, stand, and degree wheel) and degree in the used cam before you pull the chain off.
Neither are mandatory but I always like to know what was in there, how worn was it, how stretched was the chain, was TDC correct, etc. Not only do you get practice doing this stuff but that way, when something seems funny putting it back together, U will know how it measured out before the rebuild.
And of course U want to measure the cylinder bores all arond and top to bottom to check for wear and taper. Same is true measuring the crank journals.
Measure the deck clearance (watch for pistons rocking if worn) on each cylinder before you pull things apart too.
On and on - maybe it's just me, but everything I'd measure on assembly, I measure on disassembly, especially for a Mystery Motor.
Hey, it's more fun than changing brake linings in the summer or changing starters in a snow-covered winter parking lot (BTDT), right?