I'm considering going from a standard '06 diameter case head (0.473") to a magnum (0.532".) I know the extractor needs to be modified. How much does this work typically cost? I might be able to get a rare deal on a .375 tropical take-off (near new) barrel. Are there any other modifications that need to me made to make this conversion? I'm also thinking that the barrel countours may be differrent and the forend may need work too.

As you say, the barrel contours might be different, which would require that the forend be opened up, and perhaps a recontouring of the quarter-rib would be required before it counld be installed on the new barrel. But, to convert the action, all you would need to do is change the extractor/ejector, and perhaps you could just buy a replacement, magnum-sized one, from Ruger. As long as your new barrel is not so fat that it interferes with the forend hanger assembly, you should be OK. I'll bet SSK Industries could answer your questions on conversions, I understand they use the No. 1 for calibers up to .500 Nitro Express!

If you run the numbers it's not worth the bother.

Here I see #1's in .375 for $400. Your gun as is is worth that much if you had to buy it.

Besides I don't understand the appeal of a DGR caliber like the .375 H&H in a SS rifle.

I doubt the forend will fit. I think the ones in .375 are wider. It's very difficult to get a bbl off of a #1 also without damaging it's finish. The hangar can be cut..............$

I took the action from my #1 in '06 and rebarelled it to 500NE in 3" configuration.
Scooped out a bit of the forend, replaced the forend cap with a piece of rounded buff horn.
Re finished the stock and checkering and put a Pach. Decelerator recoil pad on, weighted up the stock with a bit of lead shot.
Re-cut the existing extractor and rounded off the safety button. Did not have to cut anything off the action.
Fitted a quarter rib and shallow V express sights.
Rifle shoots 540gr bullet @ 2200fps in 1.5" @ 50m. Weighs 7lb 9oz.
Have shot couple of ellies and buff with it, and some regular game.
It is one of my favourites.

I'll bet the recoil is, substantial, what??

My buddy refers to shooting it off the bench as a "significant emotional event" but carry it in the bush for miles and hours and the "lightish" weight is appreciated. I have yet to really feel the recoil when shooting an animal.

I just posted this on another topic, but I saw a #3 converted to 375 H&H from 375 Winchester at the Austin Texas gun show. Wanted too much for it. Should pay you to take it if you are going to shoot it.