your derailleur hanger should work fine with a different derailleur

again, don't even worry about cage length if your largest cog is 28t or smaller.
If you want to find out max cog and chain wrap capacity, look up RD on velobase.
VeloBase.com - Component: SunTour Cyclone

VeloBase.com - Component: SunTour Cyclone GT

you can also give yourself some leeway over these specs. Any short-cage RD I've ever used runs 28t rear just fine.
Using a derailleur hanger also increases the max cog size over spec.
Raleigh GP with Suntour VGT came with a 34t rear cog, worked fine, and the spec rates the RD for 32t max.


Here's the current drivetrain on my old Raleigh. Cyclotouriste triple 46/42/26T, wide-7 rear, 12-32t; Suntour VGT RD, Shimano 600 EX FD.
This works beautifully, just short a little chain wrap by one link, but I can use the 26T/14t combo just fine - never any reason to use 26T/12t

for gearhead weenies, here's the gear analysis