Schmeling weighed in at the 190 mark for a lot of his heavyweight fights so if he were around in 1987, he'd likely be a cruiser weight. Holy was still a bit green but beating everyone in his path plus had good olympic pedigree.
Number of rounds? Glove size? I think this could be a very good fight. Would favor Holyfield, but Schmeling was good at delivering methodical beat downs and would have a live chance, especially if fifteen rounds.
Let's say 15 rounds. You can pick the glove size. I think its a tough pic. If this were the heavyweight version of Holy, he probably wins easily. But he was far less seasoned at cruiser and not totally filled out yet.
I say Holyfield in a close 15 round decision. Schmeling would have his moments and Holyfield would definitely know he was in a tough fight afterwards.