My free tow away volvo came with almost new michelans on it, which I'd like to keep if I can, because they're worth half as much as the car. But the old brick had only been moved once in 6 years. Would sitting in the same position have comprimised the steel belting? I'd hate to find out one day in an emergency braking situation.
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Drive it like you hate it

I have heard that six years is about the "shelf life" for tires. Even though they look good, I would be concerned about the high speed curvey drive you will be regularly taking. As even Michlen says, "There is a lot riding on your tires."

I think you have a screw loose! If these were in the dark and out of the sun and acid rain AND you find no "Sun Cracks" in the side walls just drive easy at correct pressures for a time.... If you then find lumps forming that would be bad belts in the tires, but I kinda doubt it....Not on Michlin's to likely...

20 psi over ain't squat..... with cold tires just sitting... Racing I used to bump my tires to 90 psi and drive hard...... Mac

If the tires have developed flat spots, you will feel it in the steering wheel. Given the steering is in good order, it will be a slight, regular, back and forth rocking of the wheel. Not loose, just back and forth, back and forth. Think of a clock movement.
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'80 DL 2 dr

Having sat on the same tires for 6 years, I'd be more concerned with the rubber being dry-rotted. Michelins, in my experience, have less tendency to "take a set" than other tires, and they have better rubber compounds as well, but I'd definitely closely inspect them for cracking.

There doesn't seem to be any evidence of dry rot, which might be partly due to the fact that they've spent most of their life in a dark garage without the sun to eat them away. The reason I asked the question is that they look like brand new rubber, no problems passing registration with them, but I was concerned that they might be wreaked on the inside, and I'd blow one out in a high speed corner. I have a long mountain road between Home and college.

I will get rid of one of them which was still 20 psi over inflated for 6 years, which can't have been good for it. Must have been a dodgey service station pressure gauge. Well done to those clever french people for making a valve that held the pressure that well.
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Drive it like you hate it

"I will get rid of one of them which was still 20 psi over inflated for 6 years, which can't have been good for it."

I'd keep it. To me it sounds better then the rest if it held that pressure all those years. Switch it with the spare. This just an opinion, I'm not up on tires.
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1980 245 Canadian B21A with SU carb and M46 trans

If you are not a "racer" and there are no signs of cracking in the side walls, I would use them, but inspect them every so often, but at the slightest sign of wobble, I would check and probably replace the tyres. You may be lucky and get some mileage out of them.
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'86 740 GLT 2.3 injection 7 seater estate, '89 740 SE 2.0 injection saloon, '87 BMW 316 carb Coupe