Just from my own observations, the X-01 lacks the asymmetrical helmet design that the MK.I has, and the helmet is quite a lot more compact. On the left side of the forward-facing helmet the http://vignette4.wikia.nocookie.net/fallout/images/d/db/APA.jpg/revision/latest?cb=20070625092119 has a large hose going into the cranium, and a large corrugated hose that come round the side of the helmet and goes into the "cheek", and on the right side cheek it has a cylindrical HEPA filter, and the right side cranium has twin hoses that wrap around the side. The http://vignette3.wikia.nocookie.net/fallout/images/5/5e/X-01_Mk.II_Power_Armor.jpg/revision/latest?cb=20150616215806 on the other hand, has mirrored symmetrical hoses on either side of the helmet, has no cylindrical hepa filter in the cheek, and no hoses going into the "cheek" of the helmet. The reason I find this relevant is because the other power armor designs are perfect to almost every detail.
It's confirmed by Protector Casdin that the http://fallout.wikia.com/wiki/Enclave_power_armor_(Fallout_3) was the enclave model featured in Fallout 3, the Mark I, as it was seen in Fallout 2 (and Fallout: New Vegas) was not featured in Fallout 3, so the only assumption to be made is the MK.I was effectively phased out by the time the Enclave reached the east coast. It wouldn't make sense that there was no mention or sighting of the Mark I in Fallout 3 on the east coast, and then suddenly in Fallout 4 the Mark II (that was ubiquitous in Fallout 3) is gone and only a retcon of the Mark I remains, even though it had no presence on the east coast in Fallout 3. So unless there's a MK.II armor we haven't seen yet, it just wouldn't make sense that the X-01 is anything but a renamed and retconned Mark.II.
This is all extremely convoluted I'll admit but nonetheless I'll make 2 implementation versions just to give options on how people want it to coincide with lore.