Upgraded 360 Cam?
Looks like you have a Stock 360 2 bbl cam there by the specs you posted. Also those original cams by this time usually have the lobes wore down a bit and the lifters cupped. Take a look at them at tear down, you are loosing performance there too.
A new 340/360 factory 4 bbl grind would be a big imporvement.
This one on the bottom of the chart ^^^^^ .
Looks like you have a Stock 360 2 bbl cam there by the specs you posted. Also those original cams by this time usually have the lobes wore down a bit and the lifters cupped. Take a look at them at tear down, you are loosing performance there too.
A new 340/360 factory 4 bbl grind would be a big imporvement.
This one on the bottom of the chart ^^^^^ .