I owned a swift and I don't think it can handle much power. I think at the most you can do a Sidekick engine swap(1.3 to an 1.8L) but the tranny is the weak link(I had to replaced the tranny once with my low output 4banger not the GT model). Anything else you would have to do a custom engine cradle but the frame is weak so there is alot of flex.
Check out http://www.puresuzuki.com/suzukimain.htm as they use to have Swift hop-up parts but it appears they have a dead link now on their homepage.
Parts here too: http://www.hawksuzukiparts.com/
Some Swifts who race in the pinto class:
http://www.zukiworld.com/month_080102/feature_4bswift.htm
http://www.zukiworld.com/month_070101/feature_superswift.htm
http://www.zukiworld.com/
Jay Leno put a v8 in the rear of a Ford Fiesta so anything is possble.
I think there is a reason I don't drive a Swift anymore but a AV now. I don't miss those 50MPG days at all in that death trap.

Would be fun to race one though.
Good Luck,
Con