Yes, there is a lip on the guage housing.
What I did:
Each guage has a cardboard sleave that slides over the main body of the guage. This carboad piece makes for a great template to the size of hole that is needed.
Yes, the inside metal piece is what I cut. GM has grooves and circles on this piece of steel. So it is easy to find the right place to set your template on and draw a circle on the steel by using the INSIDE of the cardboard sleave.
HUGE TIP from Greg that saved me. Put your circle as far 'down' on the steel plate as you can. You will see what I mean when you start doing it.
as far as mounting the guages, I simply used the mounting hardware that came with the guages.
Except for the Tach. The tach's supplied retainer bracket was too short to squeese the guage to the metal plate. So I got me a small pice of steel,OSH store, bent it and driled the two holes for the guage mounts..worked great.
Hmmm, the wireing was all soldered(sp?) It was fun routing all the wires to one side, lableing them and using that 15pin socket too. You will need a pin crimping tool to make the socket work. I use to repair copy machines so i already had one and knew how they crimp.
Oh and I used Auto Meter replacement bulbs/sockets to replace the facotory buld/sockets that run off that circit board thingy that GM used. Wich reminds me, that circut board thing is your wireing digram also, I simply followed the path of the copper to figure out how the factory stuff wired up. Then replicated the copper path with wire /forums/images/graemlins/thumb.gif
Hope this helps and was clear
Good Luck /forums/images/graemlins/peace.gif