Don't let anything happen to that selenium rectifier and if it does, don't breathe the fumes from when it burns. Those are pretty common on old 1950s jukeboxes and other hi-fi gear, and are notorious for burning up and being super toxic while doing so.
If you just want to replace it, finding some high-amperage silicon diodes will be pretty easy. You could probably use the diode bridge out of a 10SI alternator without too much field engineering.
