This may or may not be a concern. What is your oil pressure? The older engines only had 40 PSI versus the 60 PSI found on the later 1965 & up GTO's and HP engines. If you only have the 40PSI pump, then I would be a little hesitant to push the power through it - but keep in mind I am no expert on this and I would contact Butler or Kaufmann who build these engines regularly.
That said, the 421 as Bear stated should have no problem hitting the mid-to-low 13 seconds. Keep in mind that the 1964 "389" used by Jim Wangers was fitted with a disguised 421CI that was blueprinted with the "Bobcat" kit and ran 13.1 @115MPH in the 1/4 mile BUT, it was fitted with a close ratio 4-speed and 3.90 gears. So, my guess is that with your combo you could get a realistic mid 13's. Maybe fine tuning would drop this to lower 13's. The 0-100MPH times were 11.8 seconds and 0-60 was clocked at 4.6.
The above performance was with a "Bobcat" prepped engine which meant cc'ing the heads down, and thinner head gaskets to achieve more like 11.5 compression ratio - way too much today unless you are OK using racing gas only. Your compression now is probably 10-to-1 and requires a blend of race gas or an additive.
You cannot use the later heads IF you are not going to do a rebuild and 1.) install matching pistons for the later heads, 2.) bore the cylinder over to the 428 size so the larger valves do not hit the cylinder wall or get shrouded.
To improve performance, I would increase the valve sizes to that of the Super Duty 421 if they can be fitted. The #77
's have 1.92" intakes and 1.60" exhaust. SD heads used 2.02" intakes and 1.76" exhaust. I might go with the more readily available Pontiac 1.66" exhaust and use more cam duration on the exhaust. Some will install hardened seats on the exhaust at this time, but that is often a personal opinion as to the need. Use a good 3-angle valve job and port match & clean up the ports of any rough castings or casting bulges.
Install screw-in studs and matching springs/retainers to go along with your cam specs. If going with screw-in studs, you will want to use poly locks to hold the rockers in place. You can go with stock stamped steel 1.5 ratio rockers or roller's, but make sure you have the rocker arm balls with the oil grooves - not the smooth style. I would have the valve-to-head clearance measured so you know exactly what the limits of the cam lift will be should you choose to go higher on the lift than the factory .406" used in most instances.
Ram Air exhaust manifolds are good, but I bet you have the 2.25" diameter outlets and pipes? The 2.5" outlets would be better as would be 2.5" pipes and free flowing mufflers. You want the exhaust to breathe easily and not be restricted.
Dial in your distributor curve.
Now all this is food for thought and is something you can use as a baseline and go from there. I would do a little more research and find a machine shop I could discuss my options/work with. If cost is not a big concern, then you might want to contact SD Performance as they have a package that will rebuild your heads for big improvements in flow and HP: SD Performance- Pontiac Performance Specialists
Others to contact would be Butler https://butlerperformance.com/
, Kauffman Kauffman Racing Equipment
, and Nightmare Performance Nitemare Performance | Custom-Ported Pontiac Cylinder Heads
depending on where you live.