why the SSM90 kit sucks (in my opinion):
- single belt setup
- can only run an SSIC because of [edit: injectors, i guess]
- the pulleys are way more expensive and hard to find
- you are limited to pulley sizes and you'll eventually run out of room to grow
- the price tag
if you can get over those things, then you'll be just fine with an SSM90 kit. otherwise if you want to actually go somewhere with your setup a top swap is much more capable of supporting an actual build.