Mr SS,
64elcamino is correct. The 64 dash is "flat". I have found that it you use a die-grinder and hog out the larger holes a bit they will accept a full 5" "monster" series tach and spedometer. It looks awesome, and a great costom touch to the panel. I also mounted 1 5/8" gauges in mounting cups hanging upside down just off to the right.
Both dashes are interchangable in both years. The 64 is easier to customize. But I did leave the stock radio and clock. looks cool!