It's not a large distance off. Probably you can make the hole in the hold-down oblong enough so the distributor can be turned counter-clockwise just a bit and get it in spec. Make sure you rev it above 1500 and then let idle again between taking readings (which should be consistent).

You can also replace the hold down with a small block Chevy distributor hold down. Then you can turn the distributor to get cam sensor retard in spec. But make sure the distributor gear is good.

Either method requires removing the distributor.

Easiest thing is to mark the rotor position on the firewall and put the distributor back in with rotor pointing exactly to same place (may have to turn oil pump shaft just a bit with a huge screwdriver to get distributor to drop down all the way). Gears are helical cut so they turn as you drop the distributor in.

Alternatively, you put the engine on TDC#1 and drop the distributor in with the rotor pointing to the number "6" cast into the top of the distributor body and the cap (if you put it on) with terminals pointing out 90 degrees to the side.

Either way, if your cam sensor retard is close, then distributor is in right and you can turn it a little from there to get the desired cam sensor retard.

Good luck and best wishes for a successful repair