The rims and tires on my 1966 LeMans are too big. I don't want to modify anything and I'm wondering about the largest rims and tires I can install. The car has been updated with disc brakes. I am thinking that I can put on 16x7 rims with zero offset and 4-in backspace. I am looking at 16-in 235/50 tires. I would certainly appreciate comments about how this might fit on a standard height suspension system and no modifications to wheel wells. Thanks in advance!

Would be best to take he car in to like a Discount Tire.  They can measure backspace/fender clearance.  Even if you don't buy the rims/tires from them, you will have the spec's to take some where else.

An 8" rim is about the limit of GM A-bodies without outer and/or inner fender modifications.

You can also purchase a wheel/tire measuring tool from the Jegs or Summit Racing if you don't want to go to a tire store like Jusa suggested. These are $100 or less. They will tell you back spacing, offset, and how big a tire you can run in each fender well.