YZ/DT compatability

Ok so ive been thinking up ways of improving the DT's performance off road, my main gripe is that the suspension is very obviously setup for road use, and is far too spongey and wallowey for my liking off road on jumps etc.

Been talking to a mate who have owned a YZ and he said that the swingarm, rear shock and front forks should all bolt up to the DT... is this correct?

And if so, will the DT wheels fit the YZ gear? Been told the speedo drive wont work so will need a digital speedo with magnetic drive, and that i will need longer cables making up, that side of things doesnt bother me, just wanting to make sure everything else will work?

If not, any advice on other parts i could fit etc would be grand!

I have been told that refilling the front shocks with 20w/50 engine oil makes them considerably better