JB should have a "split bowl". Droop should bolt on.

The last pro I know who was doing that conversion was Jack at MPD in Costa Mesa. he used to do them in the off season but I read a while back he had discontinued that service. Considering the cost(approx $350), a used split bowl is probably a less expensive alternative.

Slightly better, yes. Probably nothing the recreational user would notice, performance wise. There are even 2 different versions of the JC bowl and one is preferrred by those who have converted the bowl for racing use. Only a little difference, but important to those for whom a few tenths of a second  might count.