Forgot I'd already made this post! Sorry for the late reply and thanks for the help.
I'm actually asking about Indian models, so I guess this is kind of the wrong place. I suppose whatever the method, the loss of performance will be there.
Too bad--I would love to have a Fireball based on one of the older Indian bikes, but would really prefer a left-side shift.
Actually, you could do it with an older Indian-made iron Barrel bike, but you'd have to update it.
The less desireable but functional way would be to buy the export left shift linkage kit for the models that get shipped to the US. This will work on any 4-speed Bullet.
The better method all around is to convert to the 5-speed gearbox and a 5-speed engine case that has a kick-start-only primary case These are kind of hard to find, but you can find them still.
Build your Fireball on that engine and transmission, and put it into your old Bullet frame.
Sell the old parts that you don't use, for some funds to buy the case and transmission that you want. The end result is that the 5-speed is a really nice transmission with good gear spacing, and it has a very good left-side shift thru the engine with a nice positive single shaft shifter which is real nice.
It will probably cost more money overall to do it this way, but it is a very solid way to get your Fireball built with later model parts that will fit into your frame, and you'll have a very good left-side shift and a real good gearbox.