DTRE/X are the same as the DTR except they came with an electric start instead of a kicker. The stator and cranks are therefore different but everything else about the engine is the same.
It's only the 4GW TZRs and 4DL TDRs that came with the 4FU cylinders to my knowledge. There may have been other designations that came with 4FUs but none in DTR configuration.
I always wanted to try it out myself and a few units back in the day. Never did though, I am happy to park DTR development for the time being, happy enough with the Athena 170 kit for the moment.