I am currently awaiting the manufacture and delivery of a 6.5 RM barrel. I have a couple of .264 WM rifles but never considered trying to make 6.5 cases out of them. The 6.5 is so much shorter... I did however find 150 Remington cases and plan to use that. I am encouraged that Remington may be making them again, but I sure could not find anything in stores in Canada.
For dies I bought some used RCBS FL and seater dies from the same guy I bought the brass. I have honed out the neck to reduce the working of the brass, and have the decaper and expander ball internals from a Forster 6.5x284 on order to replace the RCBS guts. I prefer the expander ball location in a Forster compared to a RCBS, and the availability of different ball sizes. You can see the
details of the die mods here. Thanks are due to helpful advice from other contributors here.
I would suggest you take advantage of the Remington brass at Bruno's to considering resizing. I found the Remington brass while a bit thick in the neck to be of quite good quality. See
this thread for more detail.
My plans for powder is to try H1000 and VV N165. No experience of course. I primarily based it on 6.5x284 cartridge loading, as 6.5 RM data is a little harder to come by. The 6.5x284 is about 2 grains smaller in case capacity, so the 284 loads are a little lighter...