Most radars couldn't, not like modern radars at least. Some could tell "high" or "low". More "accurate" altitude measurement could be done with a special separate radar that was scanning vertically and measure altitude on a particular target. Even that was not very accurate and at long ranges could easily be off by a few thousand feet.
well dont need to be very accurate it can be something similar:
1. contact: estimate alt : between 12k -20k
estimated speed : 250-280 mph
current heading : 270 etc...
that way there will be still some mystery to it but defenders have a lil more info on in coming contact. And also they can make it so lets says those info will be available if contact is above 10k and
a continues contact for lets say 1min...
so if you blink the dar only for 30sec, radar wont be able to show any info on you because it wont be able to collect enough data.