One small problem, the damned things are so differently shaped, plus they obviously use different internal systems because they confer different radiation proofing, use different power plants, different hydraulics/servos and so on.The underlying frsme makes more sense.
And I mean, a lot of things are the same on the inside. Especially military wise.
A T72 and a T90 are the same internally for the most part.
Same with power armor. It isn't identical underneath, the frame os just a place to put it on.
T-45 vs X-01 is less like T-72 vs T-90, and more like M-47 vs M1A2 SEP V3