Are they Lenso S7's? If they are 4 stud they will probably be 18x7.5, it should be on the inside of one of the spokes along with the offset. If this is the case 215/35r18 should fit fine.
I have 17x7 on a 180b with standard struts, +40 offset wheels and 30mm bolt on spacer, giving a +10 offset.
Hope this helps.

In regards to the stretched tyres there is a legal requirement for wheel width. ie 215/35r18 has a recommended wheel width of 7.5 and is permitted to go on anything from 7-8.5. (not to mention issues with spacers, track width and wheel size etc.)

_________________
http://ozdat.com/forum/viewtopic.php?f=33&t=17911

Not all cars look like sake boards when fitted with big wheels, on here it's not everyones cut of tea but hey if you wanna do it because you want to go for it man!

IMO they do need to come out a bit also you will notice that they will scrubbt he top of the wheel well and guard so you might need to run more neg camber, wont know this untill you have the car closer to the ground, but yes it can be done and I have done simillar before without making the car look stupid.

I know it's not a Datsun but this is what my old teg looked like with 18x7s 205/35-18 Falkens

_________________
"You stay classy OzDat"

Can you go a slightly lower profile on your tyres (not like there is much left to go down to when you are already at 35 profile on an 215 18!)? It looks like you need to buy new tyres either way.

Just because the rolling diameter of that tyre and wheel combo will be slightly bigger than the OEM wheel and tyre combo. You should run into minimal issues if the entire 18" wheel rolling assembly has the same outside diameter as the original 14" one.

I'd not go wider than the 215s, at least not on the front, or you'll end up with more scrubbing issues not less. Hell i'd not be past putting a 205 on there, depending on your wheel width and so on. If they are indeed only 7 or 7.5" wheels (which seems likely given the large positive offset of those wheels and that they were likely originalyl intended for a front wheel drive car) then a 205 should go on ok.
Stretch isn't for everyone but extensive experience with it tells me it does nothing to make your car handle any better or worse. Also as you go down in profile the more marked the stretch appears, simply cos the sidewall is lower. 195/55R15s on my 7.5" wheels doesn't look that stretched at all but by the time you get to 18s tyres often look stretched.

_________________

If you bought them at a "crazy" price, then resell them, make some cash and buy some 17"s... Saves some issues and you won't need to necessarily buy new tyres.

_________________
Daily Drive: '80 200B GX Wagz
Soon to be: ... Supercharged? Can't ever decide..

If it's not broke, don't fix it.. Upgrade it!!!