OK friends here we go - this weekend I am going to remove what I need to to get all my guages out (including speedo and tach) - two questions for all of you.  #1 any advice - I am a novice wrench and this is the first time I am attempting anything of this magnitude and really don't know how much I need to remove to access these.  #2 my vette has a metric speedometer and I was able to find a 140 mph standard (if that is what we call whats opposite of metric) speedo on ebay - I am going to try and swap those two - any one with any experience doing a speedo metric to standard conversion.? All advice appreciated as always.  Ken

Ken, just take your time, and take a few pics of the disassembly as you go, if possible. It will help.
You'll probably need to lower the steering column to get the speedo/tach panel off, but it's not too hard to do. Just remove the lower trim cover under the column, and you'll see the bolts/nuts that hold it to the dash. Remove the fasteners, and the column will drop far enough to let you get the dash panel out easier.
Label/mark all of the connection as you take them loose from the back of the dash, so you'll know where to replace them.
Check out Dave's thread on getting the speedo cable loose from the panel...
From what I heard, the speedos that are being sold for this conversion are plug & play...already calibrated and such. It should just be a remove/replace deal.
hth

Thanks - I'll give her a go.

I know of two sources for speedo repair/conversion.  1.  Corvette Clocks by Roger.  He does excellent work and if you ask first, he will tell you if he can do the conversion.  2.   Red Line Gauge and clock Repair.  He also does outstanding work very quickly and will spend all the time necessary on the telephone to help you solve any gauge or instrument issue.  I would deal with this guy first.  Google either to find them.