Ok so I'm going to try and be a little mature and take all the off road parts off my second 90 and get it back to standard.

Currently it has modular rims with bf goodrich muds on it and I'm thinking the cheap and cheerful option is to buy a set of disco standard alloys but hold on a minute, which ones fit and which ones dont.... I recall seeing an awful picture of a butchered alloy on here once upon a time.

Im not sure what makes a "boost alloy" genuine and what doesnt. What other options apart from standard defender steel rims??

if we're talking about the 1989 90 in your signature, then disco 1 freestyles will fit.

Standard steels are a cheap option, look well with a fresh coat of paint.

Has it got disk or drum brakes on the rear? I bought 5 boost alloys for 35 quid a couple of months ago

All depends on the rear brakes I think. There's some information out there that suggests boost alloys fit rear drum or Salisbury type axle due to being different but as you can see here are a two wheels, a 2009 boost from a defender and a cyclone from a disco 200tdi. They're exactly the same where it matters. There are a few types of Boost Alloy - the original type as fitted to the Discovery 300tdi XS of which I just sold a set:

Commonly simply referred to as 'deep dish' alloys, the later type fitted to the last of the Discovery 300tdi ES Premium - which are the same as but a different colour to - the most popular type that were fitted to the more recent defenders of which there's loads on eBay (including this one).

Disco steels were cheap and plentiful but are getting thin on the ground and no longer 99p a set because people want them for trials etc and look better than modulars.

H/D / Wolf wheels are my preference but they weigh a ton!! You also need the longer studs, at least on the rears.

it's all about PCD!

Everything mentioned so far shares the same pcd.