My 340 is close to yours but I run a ported X head, little more cam and a 800cfm carb.
My initial timing is set at 16 BTDC and have 18 degrees of mechanical advance.
All in @ 3200 rpm
My engine has 14 inches of vacuum at 800 rpm idle.
vacuum advance is set to add 10 degrees @ 3200 rpm
16 int + 18 mech + 10 vac = 44 Total
My car is for street use and I burn 91 octane pump gas
Engine runs very well, starts nice, idles great and has never detonated.
If I make any change it my be to add more vacuum advance.
