I used them on my old 6m6 a couple years ago. Worked out great. It's just a template for widening the exhaust port and cutting the intake side of the sleeve. Nothing drastic, and it WILL improve performance over a stock cylinder.
Now if you want a real port job go talk to Chuck at Team Scream. I have ridden one of his ported 61x cylinders... WOW, you won't get anywhere close with the race-logic templates.