I recently rebarreled an old Model 12 with a 30″ – Stainless Select Match – Small Shank – Bull – 308 Win – 10 Twist drop-in barrel – from Northland.

It is NOT slender, but it shoots bughole groups with Berger 155s over Varget. It (so far) shoots about as well as my Savage Palma gun.

The 10-twist will also enable you to shoot longer bullets if you like. I have only tested with 155s since that's what I mostly run through my Palma gun.

I have not found any better value proposition anywhere yet.

Northland also usually has large shank barrels.

Good luck.