Soo... I gave the Lithgow to a friend, as reported earlier. Then a guy here on gunco made me "an offer I couldn't refuse" on a Longbranch barreled action. And I found that Sarco has Navy Arms .45-70 Enfield barrels for $85, and... a quick phone call, and one is on the way.
Apparently (possibly?) Navy Arms used both No1 and No4 actions; different reviews said No1 and No4, anyway. Some other sources claim the tenon threads are different, some say all SMLE threads are the same... looks like I'll find out for sure soon.
Looks like two switchbarrel Enfields will be built in parallel. I have a spare barrel, so it looks like I'll be starting with .303 Epps (basically .303 Ackley Improved; I can rent the reamer for $35), 7.62x54R, and .45-70. Bob wants .410, .45-70, and 7.52x54R to start with, though I'll lean on him to pick up a spare barrel so I can chamber it for Epps while I have the reamer here.
I keep looking at the Beowulf reamer sitting by the keyboard, but that's outside the safe range for an SMLE action. On the other hand, .50-110 would be doable...
The Enfield's unusual flat bolt face and generous extractor travel means it will feed various different rims without need for modification. I've even found a few reports of people who converted their SMLEs to 7mm Mauser, and there's a company out there right now doing conversions to 7.62x39.