CHRISPY

I would vote Vortech with a 2.5 pulley non aftercooled.

Do up a custom front mount air to air cooler and you are all set

Blown98

Put me down for Vortech, i have had one for a while and im making plenty of power on a stock motor. and it fits under the hood.

S_J_H

Both kits in stock form have pros/cons.
I have a modded G-trim system and like it a lot. If I had an ATI kit I would probably mod the heck out of it as well.
The Vortech G-Trim will make very good power if you spin it fast.But I admit you need to spin it to or beyond it's redline to do it.
The Vortechs belt drive system is superior to the ATI's kit IMO.
If you can't spin the impeller properly because the belt slips or the brackets flex then you don't have much to work with until you fix that issue.

The Vortechs belt drive design will allow you to make very good power with only a pulley/belt change providing you have the rest of the equipment needed to support it.
I was running 125+ mph traps with 2.73 gears + 2800 Pi converter and close to 3700 race weight with stock heads and stock 98 cam and stock Vortech plumbing.
Been making changes recently.:-)
I should have a pretty hardcore G-trimed 348CI setup running shortly.
2.5" pulley, custom 4" inlet ducting, custom 2.5" outlet ducting directly to the throttle body( no intercooler),alcohol injection and completely redone fuel system amongst other things.
I expect 130+ mph traps and very low 10's once I put a slick on it.
Steve