This part of your advice kind of lost me: "surfaces spotfaced to the same
thickness as the intake manifold".

Can you explain what spotfacing is?


If you have changed to a later manifold you may have to use some
half-washers to get good tightening on both. I took my FI exhaust manifolds
over to the machine shop and had the bearing surfaces spotfaced to the same
thickness as the intake manifold to make assembly a LOT easier.

Blown-gasket

We don't know what vintage your engine is. Join our board and post your specs as part of your profile! Could be early: separate intake and exhaust manifolds, with both bosses where the large washers bear being the same thickness. Could be '67 with onepiece intake and exhaust. In either case, disregard George's comment above.

Could be later or upgraded B18 or B20 with separate intake AND a later separate dual downpipe exhaust manifold from a fuel injected B20, or chopped '67 onepiece (breathes better). The bosses on the exhaust manifold are thicker than the bosses on the intake manifold, and so you have to "shim" the intake with 1/2 washers under the retaining nut to get even bearing. What George has done and what I'll get around to doing, is taking some meat off the surface of the exhaust manifold that bears against the gasket and head ('spotfaced') so that it's the same thickness as the intake manifold.