I'd love to see your build...you'll have some issues with the tire clearance and the seat post tube and you probably won't be able to fit anything bigger than a 25...I did manage to get a 28 once (can't remember the brand) bit it measured less than 28 of course, and there was only enough room for a business card btwn tire/tube.
I'd like to see a pix of your build when you're done...
christian