Thanks for all your suggestions and advice.
I replaced the distributor cap and rotor, it didn't stop the backfire so I'm going to try some of the other suggestions when the weather warms up here a little bit.
I'm still leaning toward a cam problem but it's just too cold right now for me to investigate that further.
So, thanks again for all the responses/advice, I meant to reply sooner but life got in the way.
