Luke, 255 on 7.5" rim?

Can anyone advise me on the following combinations:
255/40/17 on a 7.5" rim or
245/40/17 on a 7.5" rim.
I've got the 255 mounted on the rim fine I'm just not too sure if there may be problems with the sidewalls. I've mounted them on my 124 and have enough clearance to avoid rubbing. I know, I should have at least an 8" for these. But hey, they're free so why not? The wheels are 17x7.5 et35 Monoblocks from a 97 E420. They are actually 202 wheels. Both of the above tires are Michelin Pilot Sports.
I would like to put the 255 to rear and 245 to front. Either this, or wear 235/45 Goodyear Eagle F1 , which I'm trying to avoid.
Would this be unsafe? Anyone ever try fitments like this? Any advice is really appreciated.

Thanks,
Bill
91 300E