fxr trans mainshaft upgrade?

[86 FXRC]

I have a 86 fxrc and I want to upgrade the trans to the splined shaft vs. the tapered ( I found out that it wont hold up to a good burn out). I have been told that there is a kit but I cant find it online. I do have a guy that has a splined shaft gear set off a 87 fxrt and that has to be the upgrade (I think)? If that is correct I need to know what clutch basket will fit. I know the starters changed in 90 so i dont want to go changing inner primary and starter. could I change the ring gear or the starter gear? any help would be fantastic or am i just

[springer-]

Bikers Choice used to have a kit. I know they discontinued it for a while because of avialbility of parts but I think they may have brought it back. An alternative is replacing the entire transmission, primary starter etc.