I would buy one for about $250 $350
If the Model 51 is in very good condition it should bring $250 - $300.
Send me your email & I'll send you a scan of the Ithaca model 51 exploded view & bolt buffer.
An Ithaca model 51 magnum 3 inch shotgun is worth $275-$325, depending on condition.
Best to let a gunsmith do it.
go to a sight www.corsonsbarrels.com ==New Answer == Or look on Gunbroker.com. I have seen these barrels there frequently.
just soppose to pull out
Technically they are both "Featherweight", but the Deerslayer had a shorter barrel with rifle sights for shooting slugs or buckshot. It could also be fitted with a scope.
it is 20 ga