Sorry I haven't been around this week much. If you want to go cheap - you can do spur side spring mod yourself by just replacing screw holding outer slipper plate with grub screw of appropriate length - of course you should thread lock it in place. Then you have to use some washers on gear side where spring was as there isn't thread all the way down to gear and add just nyloc nuts there so it stays in one piece. What is next step is quite obvious - put washer, spring and another washer on newly mounted grub screw and adjust everything with nyloc nut on the end. You'll might have to drill small hole in undertray due to long grub screw or you'll shorten it so it doesn't rub on it.
Then you can use
http://www.racing-cars.com/pp/Produc...ist/U3846.html instead of alloy/plastic gear. Is it really worth it? Full steel pinion upgrade conversion for SX1/2 is about the same as just the steel gears for original layshafts and there is no hassle with sourcing grub screw and any other additional work required. So it's up to you to decide what you want.