What Ironsight said. The slides are basically HiCapa slides.
Outer barrels work but the slide may need a bit of filing.
Recoil spring, inner barrel, BBU are inter-compatible. The TM hammer spring is too short but I've used one by spacing it with a BB (i.e., drop a BB in under the hammer spring).
With minor fitting you can use a TM aftermarket trigger, although as mentioned the trigger bow is not compatible.
The WE 1911 can take real steel grips (I put real wood grips on a 1911 and real Pachmayrs on my WE MEU).
In my experience the barrel bushing is compatible with Western Arms' but I recall someone telling me it didn't work for them so YMMV.
A peculiar combination I was able to get working on my MEU was the stock WE slide, made-for-TM aftermarket barrel/chamber (Guarder) and a real steel barrel bushing. The RS bushing fits in the WE slide, but the stock WE barrels are slightly (<0.5mm) too thick; the aftermarket outer barrel was marginally slimmer and worked fine. The TM outer barrels are about 1mm longer than the WE ones.