Also I was thinking of doing a leak down test. Does the piston have to be at TDC or does it not matter since the rockers are off and all valves are closed.
I would just skip the task of the required reassembly of the valve train in order to do a compression test and just follow your original instinct of doing the leak-down test, as it will generally provide greater evidence of any problems.
Generally, one would want the piston at the top of the bore as this is where the greatest sum of wear to the block bore will be evident and provide the most accurate insight as to the overall condition, though this is a little more challenging as one will need to place the piston pretty darn close to T.D.C. each time, otherwise the air pressure applied will push the piston down the bore, sometimes quite abruptly (don't leave the turning wrench on the crank shout!
)! But if one where chasing just piston and ring component issues (i.g. broken rings and/or piston ring lands) it won't make any difference.
It is actually easier to do the leak-down test with the valve train disconnected, as one wants to be sure both valves are closed anyway; and if one detects evidence of leakage thru a valve, then one can more easily, with say a soft-metal drift and hammer, rap on the valve tip to attempt to upset any particulate material (i.g. carbon) that may if only be temporarily be not permitting the valve to fully seat.
Also, not so much with broken rings but rather with failed piston ring lands, the sealing capability may vary depending on the luck-of-the-draw as to the ability of the segmented land section to perhaps if intermittently to provide support to the ring(s), so sometimes in suspect instances we have found that double testing at both top and bottom travel positions may reveal something askew, or just more confidence in the observation.
Scott.
