I didn't look too hard but suspect this might be a straight swap
I can't see why not. Maybe I am missing something. Feel free to shoot me down in flame if you spot anything wrong. I am curious to know if I have missed something
The OEM part number for the 100HP rear axle is 51856918; that isn't included in the list of Reference OEM part numbers in the ad you linked to.
literally was the first I found with Google images, there might be better deals out there
I think this guy is just a dropshipper.
I don't see how this is any different to the
IM axles product, apart from costing more.
IM axles state specifically that the beam is for drum braked models only. They do make separate beams for the disc and drum braked 500's; I'm surprised they haven't made one for the 100HP, given that quite a few folks will want to keep these on the road beyond their design life, and doing this will likely require a beam replacement at some point.
There's two things I'd try before writing the car off.
The first is to give IM axles a call and find out if they know what's different about the 100HP beam. You might even persuade them that it'd be worth their while adding one to their catalogue.
The second (and the results of doing the first may shed some light on the feasibility of this) is to just buy one for drum braked Pandas, and do whatever needs to be done to make it work with the 100HP. I'd imagine this is likely to be easier than repairing a well rusted old axle.