I will agree with you that the OP has to consider that a 245/45/16 is 15/16" smaller than the stock 225/60/15 (stock tire size for 1985, this car was not calibrated to the ponies), but not "more than a full inch shorter than stock". Yes it will affect speedo calibration, but being a mechanical gear/cable setup is not 100% accurate to begin with (take a GPS with you in a said stock car, my speedos have been off 2-4mph at cruising speeds).
The O/P's original question wasn't in regards to the 15" wheels. He asked about the 16" pony wheels. Stock tire size on the 16" pony's is 225/55/16. Going with a 245/45/16 leaves you with a difference of 1.06”. Last time I check, 1.06” was more than an inch?
Even if we did go by the 15” wheel and tire specs, the height difference between the stock 225/60/15 vs. a stock 225/55/16 is less than 3.05mm….total. That’s a difference of 1.525mm height in the sidewall….miniscule. Most guys burn the much rubber off of their tires within the first month of owning them.
That one inch height difference between the 245/45/16 and the 225/60/15 or 225/55/16 may seem insignificant when we’re talking speedometer calibration, but that’s over 4% of the original height. That’s 4% slower you’ll be traveling in comparison to what your speedometer is reading..That’s a 4% loss in fuel mileage and an additional 4% gained in total mileage over the course of the year. Since the average person puts on approx 12,000 miles in that time span, that’s an additional 500 miles (approx) showing up on you odometer that you never really put on. Add the aforementioned loss in ground clearance (which lowering spring and long tube header guys will appreciate) and it moves form insignificant, to inconvenient. If all that is worth running a shorter sidewall to you for the sake of looks, then by all means go for it. Just remember there are consequences.