Very nice write up!

Here's my 2cents that's been gathered through the years. Hahah, i'm not old. But anyway, I have done research in this and played around with differing wheel and tire diameters, widths, offsets, you name it. I usually play around on this website. The 164 that you will be dealing with, has quite a bit more room to the inside of the wheel when compared with a 240, due to the fact that the 240 has a strut type design vs. the A arm design on the 164. My thoughts with the swap are going to be that the tire will rub under very hard suspension compression (or if your car is lowered much) on the inner fender in the front. In the back and also in the front, there might be a tad of rubbing on the outer fender, which you can easily enough bend/shape to fit the tire and usually not rub. I have a friend who has fitted 17x7 alloy wheels from some of the newer Volvo R models on his 142 which is lowered. He did not have any problems other than rubbing on the inner fender over large bumps on the freeway, and his car was lowered a decent amount.(more than one inch) With the 8" wheels though, it will be getting close, if not too close, because the wheel will be about a half an inch further in that the ones on said 142, and the curve of the inner fender is not working in your favor. It might work and it might not. That's what I have to say about it, it will be close, very close. You may be able to work it without problems or maybe you will have to move the wheels out with small spacers(5mm maybe and longer studs to match), or you might even need more than that, and if you do, you will very likely need to work on the outer fenders a little bit too. And then again, you can also bang away on the inner fender possibly as well, so as to make more room for the tire.

But I don't know, best bet is to find something that is about the same size and check it out. OR, you could use the tire calculator I have above, go out and measure the space you have available with your current setup, and compare it to the numbers it gives you on this site. I can do it for you actually if you give me the tire size, and then all you'll need to do is go out and measure the space available with the current 15x5.5s on it. THOUGH, lol, even after that, we still won't know how it will do when the suspension is compressed, but we will be able to get an idea if there will be any rubbing on the front or back. And actually, i think there might be some possible rubbing on the rear of the car on the inside too, now that I think about it... I have the same wheels on my car that you do, and I don't think that an extra inch and a half or so would work on mine...

FWIW! =D Good luck!
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Kyle - www.OVTuners.org website and club Official Portland/Corvallis, OR - 1968 142 - current setup: 71b20b SUs, m40, part. stripped, custom CAI, 4-2-1 FI man., Simons exhaust... IPD sways +more