Spark Plug Change

[RMD1183]

Hello,
My son has a 1997 Safari AWD. It has about 210,000 miles on it, and I have no idea when the spark plugs were last changed - but it has been a very long time I am sure. The van has a small of raw gas when he starts it and it is missing very badly, both at idle and when he drives it. I also know that this engine has alum. heads, so my concern is pulling out the threads with the plugs, especially if the plugs have been in there a very long time! Any ideas, tips, suggestions on how best to change the spark plugs and hopefully avoid removing the threads as well would be greatly appreciated.
Thank you VERY much.

[brcidd]

Aluminum heads??/?? I've never seen one with them...

[DeltaP]

4.3 liter. Cast iron heads. Crack em a 1/4 turn, blow the recesses out with compressed air and unscrew them from the wheel wells with a long extension on your ratchet. They like AC Delco plugs. I'd be more worried of the secondary ign cables breaking. If they're as old as you say I'd replace them out of hand as well as the cap and rotor. Hope this helps ya.