I have a Model 71 that was converted to 35/348 Ackley years ago. Accuracy has declined after quite a few rounds. Considering either the 475 Turnbull or the 500 Alaskan. The barrel is set up with a barrel band arrangement so simply rebarreling it is not an option. Yes I already have a 450 Alaskan and completely love that rifle and the way it kills.
Which one to do?

what does your rifle weigh as it is now?
I would not entertain the idea of the 475 Turnbull or the 50 Alaskan if it is too light,& the rebore will take some weight off as well.The 475 is a fine round btw,I have one & like it a lot.

Shes a pretty hefty chunk now, would good to go on a diet although I've packed her around the mountains quite a bit. But I was younger..........
I'm leaning toward the 500 Alaskan as I have several molds for that diameter and Michael458 has dies in stock. The 475 Turnbull makes sense if the muzzle diameter is too small for a rebore to .500. And I like Mr Turnbull and his cartridge. Got to talk levers one night at DSC a couple years ago wih him. Delta Gun Shop would do the work.

Just put a new barrel on it. Little heavier contour from the FE cap out, to get same weight as a stock gun in 348. Just my thought is all.

I'd go 50 Alaskan to go with the 450!

There is no forend cap, the barrel was left large towards the end of the forend, milled off except for a lump which was drilled and tapped to match a barrel band. The forend is not coming off in recoil, my 450 AK was done the same way. I'd sure like to know the gentleman who did these two rifles.
Maybe I could figure out how to post a picture and show this, if it was a standard Model 71 barrel and parts it would an easy fix.