Who might be the best to get a 1965 Valiant turn/park light housing from?

Used acceptable if the contacts are still springy.

Does anyone ever successfully grind one of these apart and convert it to snap-in socket?

eBay.
Oh, that's the only problem, is a dead spring in the socket? That's an easy fix. You can get a repair kit (new spring, new contacts w/plate) from most any parts store. I'll provide the P/Ns for you tomorrow from the office.
Yikes. Don't even try. The snap-in sockets are not better! (I run an automotive lighting supply and consultation business in my off hours, and work for North America's biggest automotive bulb distributor as a day job—trust me on this one!)

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

What? These things are sealed up tight as a drum.

Thanks

OK, here's the deal: Remove the lamp assembly from the car. Push the wires forward (or dig the socket contact plate out of the socket and pull the wires forward). Carefully look at the contact plate to see if the locating tab (sticking out from the outer diameter of the round contact plate) is in line with the two contacts, or if it's at right angles (90°) to the two contacts. If it is in line, get NAPA Echlin LS-6228 or Standard/Bluestreak S24. If it is 90°, get NAPA Echlin LS-6251. You will probably want to go ahead and get a pair of these, because if the one spring has rusted or broken, the other one's not far behind. Pick up some appropriately-sized heatshrink tubing, too, and you'll need your soldering iron.



Push/pull the wires far enough forward that you can go ahead and cut off the last few inches. Solder the new wires to the old ones (don't forget to slide on the heatshrink tubing before you start soldering!) and then snap the new contact plate down into the socket. All set!

It may happen that your parking lamp wires refuse to budge, either because the outer cable boot/jacketing has grown stiff with age or because they're gunked up with undercoating, or because they're just plain stubborn. In that case, use a razor blade and carefully slice out a section of the jacketing. Make your repair, then use appropriately large diameter heatshrink tubing to rejacket the cable.

While you've got the lamps out, it's a good idea to clean the reflectors with alcohol or something else that won't leave residue, and give 'em a quick couple coats of "Chrome" spray paint from the hardware or auto parts store. And the lenses can usually be cleaned up nicely in the kitchen sink with hot soapy water and a plastic-bristle scrub brush.

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一期一会
Too many people who were born on third base actually believe they've hit a triple.

Thanks.

I'll get some micro-dynamite and see if I can get that stuff out of there!