So anyway, THIS grandpa had fun working on this and learned a lot! Here's some of the stuff I did...
1. Snugged up the loose front sight, with the help of a thin brass shim (and KWK's tips).
2. Touched up the barrel's scraped-up blueing with Brownell's Oxpho-Blue. This stuff is a revelation - easy to use, looks GREAT.
3. New breech seal courtesy of the previous owner, still working great.
4. The thin wood and shallow steel cup at the front attachment screw are IMHO a weak point of this old design - the deeper fore end on newer guns is much better. I repaired a hairline crack, fortified the inletting around the cup with thin superglue, and used a cork shim under the screw bracket to (theoretically) distribute the load equally.
5. Reconditioned the leather piston seal with an overnight soak in Motorhead's silicone/neatsfoot mix. The leather sprung back nicely and is sealing well so far.
6. Cleaned out the gobs of ancient moly grease mucking up the action.
7. Installed a Maccari spring and guide and buttoned the rear of the piston. Sparingly lubed with moly on the seal sides and piston rear, and a VERY thin coat of tar on the center 2/3 of the spring.
8. Removed open rear sight and added a period-correct "ARH 624" WIlliams peep. Fit was loose and slightly canted, but I've since moved it forward about 1/2" which seems to be OK.
9. Took off the ugly sling swivels, cleaned and waxed the stock (rear swivel stud still looks better than a hole in the wood though!).
Done fooling with it for now! Will post some numbers after I've shot it in a bit, but between the holidays and the weather that might be a while.