I'd suggest buy this from pmac might be a decent outcome.
http://zclub.net/forum/showthread.php?t=25713
Something like this then:
http://www.thezstore.com/page/TZS/PROD/classic08d04/50-2040
I have a full cover on my 260Z and it looks great. That is the way I would go instead of a cap as it covers the whole dash not just the top. The caps look obvious IMO.
Dash covers are usually fibreglass (or at least mine is) so it is unlikely to crack in the future. More expensive than the caps but worth it. Have a look at the pic and tell me you can see the joins!!!
View attachment 14740
Paul