Well, let's get some more information.
What class you thinking of running?
What kind of inline are you starting with?
Are you planning on having a crank fabricated for 180 degree throws, or running 120 degree throws?
If you're having the crank built, you'll need a custom cam and you'll need to come up with a distributor.
I love inline Jimmy's, Chevy Stovebolts and 4.9 Fords, and a T with an inline would be a very cool looking combination. But while none of what you suggest is insurmountable, for the extra cost of getting this to run right, I think your money would be better spent buying a couple of extra pistons and destroking the six, if that works for the class you want to run in.