George,
Reamer and headspace guages may set you back up to US$300 depending on who makes your reamer. Lets assume at least half that so US$150 for the reamer alone. Another US$150 for the dies ... so there's at least US$300 in expenses before you start. Now add brass costs for say 50 pieces and only one source of projectiles locally ... maybe two actually ... I'd have to check.

Call Sprinter Arms as they're local to you. Ask whether he'll make a 0.435" barrel and whether he has a reamer. That's your only barrel source locally and he may have the reamer.

The rebated rim is quite extreme and may cause issues ... but there are ways around that if your willing to think outside the box. You magazine box/rails will still need to be widened, but by going 425WR you avoid having to lengthen. That's a miniscule saving in the whole scheme of things.
Cheers...
Con