When you buy a digital dash you will find it comes with a universal plug with tails that you attach your wires to and an instruction manual
I think as far as the speedo is concerned you will be better of if you use a gearbox with an electronic drive like from agranada or s.i.e.rr.a as this will make life a lot easier
Otherwise you will need to fit a speedo pick up ontoa wheel or something
I have done it on a bike but it can be a pain in the arse