[vertigto]

So...it is the original 70 YS 400 bored 30 over with original 13 heads (a little blending), original intake, RARE manifolds and DUI electronic ignition.

If I understand correctly, with the HEI, the recommendation is AC 43 SX - AC 45 SX gapped at .045"?

[Formulajones]

Originally Posted by vertigto

So...it is the original 70 YS 400 bored 30 over with original 13 heads (a little blending), original intake, RARE manifolds and DUI electronic ignition.

If I understand correctly, with the HEI, the recommendation is AC 43 SX - AC 45 SX gapped at .045"?

The AC R 43S would work just fine in that application. You can easily gap those to .045" if you wish, don't really need the "X" plug.