If you have a 64 that hasn't been messed with (cylinder heads changed to 66 and newer) You will need a 65 4 barrel manifold or an adapter like George Posted above. 64 and 65 273's had different cylinder heads where the intake bolts on. The bolts were smaller and at a different angle than the 66 and newer small blocks. As with any modification, you will have to modify the throttle linkage and possibly brackets and if you have an automatic transmission, the kickdown linkage as well. It isn't a plug and play deal.
