Hi Patrick,
I did write Jonathan, but I'd really like to stick to carts that will work well with the Shindo's trannies, which I'm betting just have to be pretty darn good. (The rest of this thing - that is, the MM and linestages - are so drop-dead stunning that the 1st stage just has to be too.)
The SPUs you mentioned - these are Ortofon? Same thing? Unless I am mistaken, no longer made?
Lots of stuff to investigate - Lyra, Dyna, Shure (?), etc. You can read about this stuff for days on end and still feel like you don't know half of what there is to know. Of course, it's in the listening, but trying carts is the biggest pain in the butt there is.
I think you are correct about the arm as well and that is another expense. The whole venture may need to wait a bit. I still love my current setup but every time I think "it can't get any better" I am proven wrong.