Yes, that's reasonable but it will give you a set of numbers taken under the same conditions. A second run with a squirt of oil down the bores will give you another. If the figures match by around 10%, fine, but if there is a rogue one you can at least pull the head while the carbs are away. If the valves sre OK, suspicion will fall on the rings. Bores might show signs of scoring from broken ones. I doubt if you will then button it up again and redo the tests with the carbs back on, just to verify the figures. I certainly wouldn't want to waste a new head gasket unless I really couldn't make up my mind about the reasons for the bad numbers. Unfortunately with broken rings, you sometimes only find them when you prise them out after you pull the pistons.
In this case, I hope all is well and the recon carbs breathe new life into the engine.