open vs 4 hole

the short answer is: it depends

you might be able to use the plate that RRR linked to, but the holley linkage might foul depending on the manifold. in that case you'll need an adapter spacer.

4-hole v open is hotly contested and there are dyno results that favor either depending on specific sets of circumstances (intake, cam, carb, thickness of said spacer, rpm range).

for a dual plane street engine i like the 4-hole