Have a 1999 Park Avenue Ultra and want to do a sparl plug change. What are the best tools ( rachets/types and attachements ) found to be the best for changing out the three on the firewall?

Not really any special tools.
Just the socket having the rubber insert is a help and perhaps a short extension..
Be sure to twist the rubber spark plug connector on the plug to release it. They get stuck after a few miles.

I put a strip of carpet over the engine and layed over from the front. That way it gave me plenty of reach and access.

I just replaced mine. I had some Bosch Platnums that caused a idle miss. I put in some plain ol' AC Delcos.

Good Luck