Ah, the joys of standardization: we've got 1/100th scale, 15mm, 1:72, 20mm, 25/28mm, 1:60, 1:48, and so on....all of them "standards". The nice thing about standards is that there are SO MANY to choose from.....
I've got a couple of the old Revell kits myself. Judging by the sizes of the pilot figures, they're in the 1/72nd scale realm or a shade smaller. Judging by height alone, they would be somewhere between that and the somewhat larger 1/60th scale, and roughly compatible with the 25mm Steiner and Kurita infantry boxed sets (the individual soldiers are still available).
Sadly, two of the three kits were partially assembled, most likely be someone too young for the difficulty of the kits, and several parts are very obviously miss-assembled. Those will need to be carefully cut apart and reassembled properly at some point, which I am not looking forward to doing. Eventually, I'm hoping to set them up in some kind of "service bay" for an infantry scenario, with stealing a 'Mechs being the objective of the infantry raid (one MechWarrior being included in the attacking force, and another arriving with reinforcements for the defenders, so either side, or both sides, could potentially activate one of them).