First questions pretty simple, will a 4506 safety assembly fit a 5906?

Second question, since S&w no longer supports 3rd gen pistols, besides springs and groups, what spare parts should I stock to maintain 2 5906s over 20 years?

No. .45 and 10mm slides share decocker parts as 9mm shares similar decocker parts with .40’s.

Spare slide stops, side plate, firing pin and recoil and magazine springs.

If you have a (loose) two-piece guide rode then an extra one would be worth having, preferably a one-piece guide rod.

Trigger play springs don't commonly fail on the medium frame pistols but the spring & rivet are cheap & still available, so...

Don't forget magazine followers & main springs too.

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Waiting for the break of day

Tough though when your Gen III 45 doesn't even have a schematic available. If you need more than a couple of leftover springs, you either luck into a cross-reference from another model or hope nothing goes bad with yours - either way you know the end is near...

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Marty 4513TSW 13-1 642 60-10