What years of SBF clutch need dowels to center the pressure plate? I've got some 5/16 pressure plate bolts that have a shoulder on them, but a replacement flywheel I got has 8mm holes. The 8mm PP bolts I've got don't have shoulders and are smaller than the holes in the pressure plate, so I'm assuming they need dowels to center the PP on the flywheel. There's no way the PP will center with just the bolts. The flywheel I bought doesn't have holes for the dowels. All of the parts purchased were for a 1989 F-250 with a 5.8L. What am I missing?

Overall, my engine is running great, but I'm getting a minor vibration that starts around 1800rpm, goes away around 2100, then turns up and gets worse above 3k. The clutch and pressure place were taken off my of 302 that ran fairly smoothly, but has some weird bolt spacing on the pressure plate (bolts are paired really closely together). Current theory is that the pressure plate is slightly off center. Bought a new clutch and flywheel to have on hand when I tear into it to see what's going on.

Anything else I should be looking at? Harmonic balancer is a 50z Explorer unit that was rebalanced to 28oz by MPG heads when they did the engine.

Is this when driving or just engine running?

Just engine running.