Use a dial indicator or other measuring device "in the car" to measure lift, most accurate at the lifters.

If the cam is out just caliper them. You'll have to visually ID the intake from the exhaust, because they'll be different

Lifter condition is a fairly good indicator. If the lifters all show similar wear patterns, chances of one flat lobe are slim

I'm a BIG believer in keeping old lifters with the original lobe, so if you remove the cam and re-use it, lay out the lifters in order