So I've taken an educated guess and I think you are on a 3.4 CWP as this is what Pro-Motive usually supply for a 13" wheeled car. I've also assumed you are on 175/50r13 tyres.
Looking at my calculator I think you are probably running a 17 tooth front sprocket (engine jack shaft output), and a 17 tooth diff sprocket.
This means your current gearing gives something like this with a 97mph Top speed:
the spikey one 97mph top speed by Dudley Waldron, on Flickr
if you changed to an 18T front sprocket & a 14T Diff sprocket your gearing would be like this with a theoretical 125mph Top speed:
the spikey one 125mph top speed by Dudley Waldron, on Flickr
Now the front sprocket is obviously a Yamaha R1 sprocket, but the rear diff is actually a Suzuki Hayabusa Sprocket. So make sure you order the right ones. When you fit them you might have to fiddle with the chain to get the tension right.
As for handling. This is a bit of a minefield. I don't have any experience with the spring conversion but by most accounts I have heard they are not a good performance upgrade. I suggest you replace them with some "red dot" uprated rubber cones that minispares sell. Also it is important to check you have enough damper travel. For example at the front, you can do this by;
1) Taking off the damper and measuring the distance between the top & bottom bolt hole of the damper with it fully open (pulled out) and then fully closed (push it in as hard as you can).
2) Measure the distance between the top and bottom mounting bolt on the car with it sat at it's normal ride height. This measured value is your damper open length at rest.
3) Check you have at least 30mm either side of the "open length at rest" when referencing your open & closed lengths that you measured on the damper, this will confirm is you have enough bump (in) & droop (out) damper travel.
From there I would spanner check the whole car and set tyre pressures to 28 PSI all round. If you have hi-lo's, try and set the rear of the car about 25mm or 1" higher than the front. Best to measure the distance between the sill lip to the ground to get an idea of this.
Then I would take it for a GEO setup. (you could do this with your coil springs still fitted, worth a go)
As a general guide for 13" wheels;
Bit of toe out
And for rear;
Bit of toe in
Hope this helps. Good luck!
Edited by duds100, 26 September 2018 - 10:35 AM.