I'm not sure if you can get an oxford style on the Detroit last - have you checked with Carmina? You may well be able to, but I just can't ever remember having seen an oxford on the Detroit last, only bluchers.
They said they'd do any style on any last for the MTO event in NYC. I asked: What about wholecuts? "Yes". What about half-brogues? "Yes". So there we go.
I'd prefer to not do bluchers, if only because I prefer oxfords, but I do like bluchers, too.
The rain last is definitely too tight for me. The taper gets me. It's like the AE Weybridge/Cornwallis is one of the few shoes from them I just can't really get comfortable in.