I've got my new dash installed with all its extra dial goodness, but I think the speedo is out (not sure what the wheel size was on the scrapper,) any ideas on how to adjust it? Or is it easier to take the old speedo out of the old dash and put it into the new one? And if so how?

Any help/hints/experiences?

Best bet is to refit the original spedo head. Recalibrating is a job for the pros.

Is there an easy way to do that? It seems pretty tricky to get into the instrument panel

It not too bad realy - just a lot of screws I have taken them apart a few times.

Easy. If you want a run down of the dismantling let me know, Just undo all the philips headed screws from the cluster. Beware of the hidden one on the right hand side, under the metal plate!!!
AFAIK there isnt a way of altering it unless of course it has been apart in the past and had the needle taken off?vThere is a specific position the needle must go on at!!!
Cheers Adam