New manifold gasket and manifold to downpipe gasket and carb base gaskets (4 or 6 depending on if you have a spacer or not).
2 into 1??? you must have either a 3 into 1 or a 3 into 2 with a twin branch down pipe.

If you have the 3 into 1 manifold then a 3 into 2 with the long twin down pipe will really free up the breathing.

Check for compatible mounting "ears" on the manifolds (unless you opt for a 1-piece manifold). If the exhaust ears are thicker getting them ground down to the same thickness as the intake manifold is relatively cheap (or you can use your angle-grinder but I farmed mine out).

Get new nuts with hardened washers (deformed lock nuts are nice) and assume you will need at least two new manifold studs (they break).

Air horns are nice but there is no easy way to use them in the stock filter.

Carb spacers help with heat-sink issues and give a little more room in the manifold.

Check for vaccum leaks at the advance tube and windage/PCV/booster hose.

Clean the oil filler cap.

Mike!
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Mike!