Center vent is best mate. I did that a while back.
Ylui can get it out easy enough, i think if i remember rightly, i had to take the side of the glove box panel out, so that i could help push the center vents out from behind, but they should prize out without too much trouble.
I thought sod it and ended up using my vents as a frame, i basically cut and hollowed the vents leaving a rectanglular frame that was made to fit in the dash. Then i got some plastic tubing, just a bit bigger than the gauges i was using and cut small sections (2/3mm) of them and placed them up along the front of the frame, then glued in place. Then i used small pieces of plastice in between each section of tubing in order to fill the gaps, then some fiberglass, and filler, and hours and hours later and viola
http://www.e30zone.co.uk/modules.php?na ... ight=gauge
If you wanted to use your vents at one point though mate, you could always just measure the gap where they once were, cut out a large piece of plastic or somthing the same same and then go from there, either make the gauges sit flush or add some contours and shapes.
1986 Chevrolet Corvette. 330ftlb torque....V8s rule!