Note there are 2 variants of this slide – early and current, the current slides part number 11570 will have to be modified to fit the early carburettors.
If your original slide was the 8553 type and no longer available, you can use the 11570 part number but will need to machine part of the ramp off to use them with your carbs.
The important difference is the width of the stop screw ramp – please see picture:-
p/n 8553 Ramp slide 4.6mm wide
p/n 11570 Ramp slide 6.2mm wide
Please measure your existing slides before purchasing a replacement.