Would a 50-75hp Zex kit (I'd guess for 4 cyl's) work for a 125 shot with just different jets, or are the solenoids in the purple box different?

 

I just went through this one myself. I was assured by the guy at Zex that all the boxes are the same, it's just the jets that are different. Just make sure yu order Zex or NX jets, as they don't have the same taper as Holley/NOS jets. Also be sure you get the jet sizes off of the V8 jetting guide. I made the mistake of using the 75 jets that I had for the 4 cyl. kit and ended up dumping in twice as much fuel as I needed. Right now I have the 100 HP jets in and it's working like a charm on the stock fuel pump, though I have a replacement going in soon. The power comes on nice and easy too, so it does shock the tires as much. If you have any other setup questions just give me a holler.

Izzy

 

Yes, they're the same. Like izzyz28 said make sure you get the correct size jets and install them correctly.
Then have fun!!!