There are 8 but the front two are different. They are smaller.
When I made my 90 sliders I didn't do it that way. I made a large U shaped bracket out of 8mm strap - about 100mm wide that effectively clamped against the chassis rail with through bolts.. But the bolts went through the chassis so it clamped against it. We had a large debate about styles and whether to have a separate floating plate, single bolts, U bolts etc, but I favoured the through bolting method as there were already holes there and there was no way I would crush the chassis box when tightening it up plus it was easy to fit as you didn't need to get above the chassis.
I don't have a link to the guide - I can't remember where it's hosted. Someone else may remember - but I don't think you'll need it for this job really.
I know what you mean about the knocking noises, they drive me crackers. Just fixed on on mine. I just used an angle grinder though!
Chris