I’m looking to lower my Z around 20-30mm and just wanted some advice if I could still run the stock shocks and drop links etc. 

Any pics people have of their lowered z’s with height dropped and spacer width used would be appreciated.

many thanks. 

You can exchange the springs on factory springs but tbh unless they’ve been replaced it’s asking for failure. You certainly used to be able to get replacement shocks from Bilstien and KYB. 
Any lower than 30mm though and your into Proper height adjustable coil overs and you will need to go aftermarket for the camber correction. 

On my last Zed I bought some TEIN VSN22-C1SS3 FLEX Z COILOVERS from driftworks. They were really good. Driftworks even set them up for me. It was lowered about the same that you are asking for, but kept all the suspension and drop links stock. Made such a difference to the ride and handling too.

If your shocks are the original ones from circa 30 years ago then just slapping lowering springs on them will be a false economy as you'll have to dismantle it all again to replace the shocks when they inevitably fail. 

You can get OEM spec shocks from KYB and then put Tein lowering springs on them. Other options are to get soemthing like Tein S Flex coilovers from the start. They not to firm like some other brands of coilovers. I have MeisterR fitted at the moment but will be replacing them in the future as I find them too firm. 

You will also need (should) correct the camber when dropping the height. This post gives more information on using

shims to do the job:

https://www.300zx.co.uk/forums/topic/157334-ride-height-to-camber-ratio/?do=findComment&comment=1717850