That's the part I don't like about RCV 300Ms. by going to the larger dowels you can't use you old axles as trail spares with out carrying a none modified OEM hub to go with the OEM axles.
If they would have just stayed with the OEM size dowels Guys that wanted to could just stay with the two OEM dowels and stilled used your old axles for spares
As it is if you just mount up the RCV drive flange like @hisandhers80s did you don't get the benefit of any dowels.
Also it's really hard to get all 6 of those dowels drilled correctly and lined up. If your drill press has any run out the dowels can end up lose and if your trying to do it by hand well good luck with that.
Getting a per-drilled set of hubs is probably the best way to go. Unfortunately when I called Cruiseroutfitters I was told that they did not do the pre-drilled hubs.
I ended up drilling them myself and while they get the job done they did not turn out as good as I would have liked