305 heads have 58cc chambers. The major drawback for using 305 heads in high performance engines is valve shrouding. The 3-7/8” bore doesn’t allow big valves without getting too close to the cylinder walls. Fortunately the small valve heads work well on a 305 and should perform well on the 283.

You can gasket match the ports in the intake to those in the head and run a good 3-angle valve job. Excessive porting or bowl won’t yield any big gains. Be sure to use small tube headers (1-5/8”).