[Alan Roehrich]

If you're talking about the old red plastic "tool" that slips over the rocker stud, the best way to use one of those is to use it to take up space somewhere out of the way.

What you need is an adjustable pushrod length checker, Comp Cams has them. Use that on your engine, either mocked up completely (head gasket thickness included) or assembled, combined with a dial indicator that you can use to read valve lift at the retainer. Adjust the pushrod length checker until you get the correct lift and geometry for each valve and each lobe. Measure the over all length of the pushrod checker with a dial caliper, and order the correct pushrod. Thicker wall and larger diameter is better.