Well the best carb for tuneablity is the VM36-4 and Lancer here on the Forums sells the kit complete with throttle cable, a set of jets for tuning, a jet tool, spark plug plus manual.  I may be forgetting something or something/s that are also included in the kit he sells, and I've looked at all of it priced separately and he's got it at a great price.  So look him up in the Market section here on the Forums,  He's got his own Stick post at the top.

As for tuning it to run properly with a straight pipe that may not be possible for all around riding.  That straight pipe will have a very narrow power range if you don't at least baffle it. Not to mention it's gonna be very hard to tune for it, to get the mixtures right for all areas of the throttle range.  Impossible probably not,  Difficult definitely.  Lancer is the man you want to talk to on help for getting starting on some advise for tuning it with either the stock carb or his kit.  He is our resident carb man and LS650 performance guy as well. Who knows he may even steer you towards a different carb with your setup, but I'm sure he can still supply you will all the other needed parts for the conversion.

Here is a link to his market listing.

Lancer's Performance Parts

R.F.

If your intent on using a straight pipe, consider using a baffle.  Since you're probably not building a full out race motor, you won't lose the top end the straight pipe would supply, and it'll be easier to tune for low RPM street riding.  Just my two cents worth.