The Wen 909 "All Saw" used blades that were peculiar to Wen, with shanks midway in size between the 1/4" shanks common to saber* saws of that period and the shanks of reciprocating saw blades. I tried grinding down the shanks on some reciprocating saw blades; it worked, but the selection is limited for scrolling work. I was given this phone number as the number for Wen, which at one time still stocked some blades for this saw: 574-598-2203.
As to the Allen/hex wrench, unless yours has been messed with, it's a standard fractional size. Can't recall what the size is, but any decent hardware store will have a selection of L-shaped wrenches that should work fine, and replacement screws if your screws are ruined in some way.
Since the blade holder is built into the shaft of the tool, it would be awfully hard to adapt a newer bladeholder to it, although, if you've got a metal lathe or lots of patience with files, it might be possible. But it would likely be a lot of work.
Functionally, you'd be better off with a modern pro-model jigsaw (there, I'm using what everyone else uses now); it's not hard to find a used Bosch saw, and they run just about forever. You can get a huge selection of blade styles in any (decent, again) hardware store, lumberyard, big boxy store, online, etc., and the orbital action on the good saws will allow you to cut at speeds that are almost light-saber-like.
I'm sending you a private message, too, on a related subject.
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*At the time these were being sold, "jigsaw" applied to a stationary machine now referred to as a scroll saw. I occasionally try to use the historically accurate terms, although "jigsaw" long, long since got transferred to the handheld tool.