[vettestr]

Tuning is an art that is a hard taught lesson. ( !) If done without gas anylizer equip and engine loading then (2) by someone with a well rounded BLACK MAGIC approach or (3) an onboard computer. Anything less is a hit and miss deal.
(1) A dyno can load engine and monitor bandwidth to suggest departure from ideal settings.
(2) An old guy with a tuned ear and lots of experience can get you there after making changes and making a run then clicking engine off to read different loading stages. Then read the plugs for each load type where engine was ( clicked off) so not contiminated by other conditions. Here is the LOST ART or black magic.
(3) Use new electronics and multiple sensors to read those conditions (maybe making real time corrections) also called aftermarket or stock fuel injection or ONBOARD COMPUTER.
An aftermarket 02 anylizer about 80 bucks can read exhaust gas ( 1 bank only because of where installed ) but leaves many other variables not identified, just the end result. A bad plug will throw off reading as a rich mixture, cold exhaust gas from improper 02 sensor location will show as lean mixture also and improper timing or even the portion of the cam range not in powerband will be shown as rich.
Take it to local OLD GUY capable of old way results or take it to DYNO WAY to map entire loading range and suggest changes or throw parts at it until you run out of money you are willing to spend. I'll bet the dyno is the cheapest direct path with the best results for your specific car and driving conditions at those atmospheric conditions. OR install fuel injection with all the sensors to keep it within the designed BOX. Even then outside problems cab sneak up on you with any choice. I do have a high respect for the OLD GUYS and the best of them are now using electronics to fast forward or prove them right!