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You should be able to go to 205, but check with your local tire shop. Usually the guys are pretty knowledgeable if they don't have their heads shoved up their a$$e$ like my local place :\
I had 225s on my 69, I forget if they were 60 or 70 profile though. I believe the wheels were 14x7 but they could have been 6", it was so long I can't quite recall.
I've got 205's on Rally II rims on my '67. I'm sure you can go a little bigger on the back tires, but I think you will run into rubbing issues if you go too much bigger on the front tires.