Yes, even lead soldered barrels into monoblocks is strong enough, but I still like threading. Although, I have used force 44, which is not a high temp solder, and it worked very well.
As for shrinking, I seriously doubt if that would work in this application by amateur makers. I think the hoop tension of the relatively thin monoblock walls would not hold rifle barrels in place. And I have re-barreled rifles with shrunk on barrels; they always use a cross pin to make sure.