No worries Nick, I still have lots to learn after 10 years of ownership! The turbo D90's are cast and have a rather chunky lip whereas the forged CS rims have a much smaller lip. Also CS wheels are 7J front and 9J rear. Turbo D90's were introduced in 90 model year, CS rims 88 model year on turbo s. You tend to find all 89 turbo's have CS rims and very early 90's had CS rims and then later ones got the D90's. Both are pictured in the 90 year brochure. If yours is a MY89 they may be CS rims?
https://www.carsales.com.au/cars/detail ... D-4910554/CS Wheels
http://performancewheelsandtyres.com/se ... loy-whels/D90's
I've never had any issues with different brand fronts. As long as my axles are matched that's good for me. Uniroyal Rainsport 3's were quite grippy and soft and good in the wet. However find of the year for me has been these, long story short was chasing a front wheel shudder about 70mph for ages, I have a

on one of my front rims, so rocked up at a "road force" balancing place to try and cure the issue. The front Toyo's that came off were out of shape and they had these on the shelf, so we chucked them on to see if we could cure the wobble.
http://www.tyrereviews.co.uk/Tyre/Westl ... t-SA37.htmHaving never heard of them and also being £40 each (!) I was sceptical. Not only did we cure the wobble but the tyres actually perform very well. I was amazed to read the reviews on various sites where they seemed to get good reviews. Car feels good and the front grips better in the wet than with Toyo's and dry performance seems on a par.
Good luck with your choices.
Stuart