You can use a '65 4 bbl intake on your '64, assuming you still have the '64 heads. '65 4bbl intake casting number is 2465726.
4bbl heads and 2bbl heads are the same. There was no special 4bbl heads for the 273. 4bbl 273's used a domed piston to achieve the 10.5:1 compression used in these engines. The intake bolt angle and size changed for '66/'67, after which time the 273 4bbl engine was discontinued. '68/'69 273's were all 2bbl's and used a hydraulic camshaft, as opposed to the earlier engines using a solid lifter cam.
"chryslerfat" has got it right.
