Quoted:
Keep in mind you're gonna need a .458 bolt and you'll have to open up the ejection port.
I'm not trying to dissuade you. You're level of skill and access to tools may be much greater than mine, but I'd just have one built for me by SBR (or wait for Marty to come back) or buy one from RRA. If you go with RRA, you could always sell the leftover parts on the EE. I've been contemplating this route myself.
At the rate things are going here, that could take a while - as of Tuesday I have been advised to get my travel documents for two more countries in the region and that I might be here at least an additional year...
SBR should have their first batch of barrels in, but they have also been 'blessed' with a boat load of 'official business' that has pulled them away from the shop.... we're working on getting you guys some relief and making barrels, bolts, etc more available but it has been slow going (and it is difficult to move it along from over here...)