Will an original 260 flywheel work on a 302?

My Tiger has a 1980 302 #EOAE with the original 260 flywheel #C3OE-638OB. I just replaced the clutch and now have a vibration coming in at 1,500 rpm. The only thing changed about the engine was the new clutch. Looking at the old clutch cover I see that it has 4 beads of weld stacked together near the perimeter. Also, there are 5 extra holes drilled in a mounting flange opposite the weld beads. It's as if the clutch cover is intentionally out of balance. This causes me to suspect that the 260 flywheel "external balance" is less than that of a 302. I am pretty sure the old clutch came off the flywheel with the weld beads oriented toward the balance weight cast into the flywheel. Can anyone shed some light on this issue? Any help would be greatly appreciated.

The 260 flywheel would originally have been made for 28 oz-in. imbalance, and the flywheel to crank bolt pattern is asymmetrical such that it can only go on in one way. The clutch cover is generally not keyed to the flywheel, although it is good practice to replace a clutch cover in the same orientation as it was in originally.

It could be that your clutch and flywheel were at some point balanced as a unit, and there is some underlying issue with the flywheel that required additional balancing adjustment on the clutch cover.

OR: this external source says that Ford changed from 28.2 to 50 oz-in imbalance in 1981, and that's close enough to your engine date that I would worry about having a 50 oz-in rotating assembly. In this case, the engine shop may have performed the clutch cover balancing in order to bring the flywheel plus cover assembly into balance to that spec.

If that's the case you should be on the lookout for a 50 oz-in. 157 tooth flywheel. You can get them in both steel and aluminum (from places like Summit or Jeg's), and it would actually be well worth it both from a performance and safety viewpoint.