Hi me..
First of all congrats on your upgrade.

After years of living with rx115 block, there were many learnings.

Rx115 will be good with VM22 carb i e Rx135 indian carb however, I would recommend to use RX115 carb from Indonesia/malaysia for best set up. You get anything on the FB groups these days unlike I had many challenges back then. FB should cater your requirements including the head gasket as well.

Rx115 comes with 15/38 chain sprocket and 5 speed gearbox. However, Indian 4/5 speed gearbox can do the job as well. You'll need to check the plug color and tune the air fuel ratio for optimum performance.

Rx115 Carb stock jets are 17.5/130. You'll get 140 main jet that comes in for shogun and you'll need to tube to balance.
This rx115 set up is more of a mid range and above. You'll feel some slack in the initials. That's completely normal.

Hi senior...

I have finally managed gather the money for a 5 speed gear box
And I have two options:-
1)Indian 5 speed
2)Rx king gearbox

Which one should I go for?
And what should be my chain sprocket ratio?(I still haven't changed it to 15/38 it's still stock rx 100 15/39 one)

Edit:- i forgot to tell you, my bikes only block ,head and carb are 115 rest all parts are rx 100 ones like clutch bell, crank , magnet etc.