Ford Repair: low octane blues, stock ford, mustang gt

Question
I have a 95 mustang gt with the 5.0L 302 when i first bought the car i could drive it on regular 87 gas. I only drive my car in the summer and store it in the winter. When i brought the car back out the following spring I changed my plugs from stock ford plugs to NGK's, and wires from stock ford to Autolite FIT premium wires and changed the oils and filters. Then I noticed not long after I started to get the pinging of low octane, so now I cant run it with anything lower than 91 octane gas. My question is did I put in some crappy wires and plugs and go back to what it had before, or should I be thinking about adjust the timing either advancing or retarding.

Answer
Chris-

  The plugs and wires are fine...they shouldn't be the problem.  And really, the car is designed to run on 87 octance, so my guess is that the timing is a bit off.  I'm willing to bet that if you push it back a degree or two you'll be able to run 87 again...or at least 89 octane.  Hope this helps.

Steve