wat wheels would fit my datto 120y without scrubbing i have wheel spacers and i have flared the guards a little

Probably most wheels depending on your guards. I spose you don't have to run the spacers if the wheels you find are a bit wider.
I personally don't see the need for really wide wheels on a street car - for circuit cars then yeah but on the road they can be more of a problem than what they are worth.
I suppose it depends on what your vehicles purpose is.
If you just want to sit there and look at it parked in the driveway then put a set of 18x10's on it

im not sure if your aware but sigma or mitsubishi wheels fit on datsun so if your at the wreckers n see a nice set of factory mags grab them

14" hotwires will fit ya 120y quite well if on a coupe they will make it look tough as.

Any idea of rim and tyre combinations that will replace the factory wheels without using spacers, flaring the guards or anything else ?

Anything from another Datsun/nissan should fit. As well as the Sigma wheels.
So Sunny,1600, stanza, bluebird,old skyline, 240K, 200B, 180B etc.

Not sure of the sizes that will fit on a 120Y without mods though...

go the FOOLY SIK TRX RIMS maaaaaaaaaateee, they are fullly sik, too bad they dont make calais internationals for dattos, or special "cop rims" that are just normal stockies, but with the special magical power to give your an extra 80kw at the steering wheel, double that if you have a nismo sticker bigger than your back windscreen.. seriously tho, go for something like hotwires or bathursts, or even globes something like that, super lites look quite good, as do watanabes.

yeah mate go for the superlites i just put some on my ute got my centre caps i was waiting for today looks pretty smick ive taken some pics ill post em next week