The kit from koster is $18.95 plus shipping and you email Bill Koster directly at this addrerss.
wkoster2@comcast.net
The kit has 3 options for forward firing .50's, 2 of them are single .50, and of is twin .50. There are 2 options of G model nose cones, and one that can go either F or G model. A nose cone for D and E models as well.
I have a few ideas I'm kicking around for this kit, I might be able to get 3 17's out of it.