At Cruiserweight,I take it ? This would have been a classic,and Holyfield would have had his arm raised after 12 or 15 rounds. He would have been too strong and busy for Spinks,imo. Michael's Spinks Jinx would have caused a few problems along the way,though.
I am going to give Spinks the slight edge.. Although we never really saw him fight at CW, he did compete at the highest level both above and below that division, so 190 lbs, might actually have been a good weight for him. In 1985, Michael was still in his late 20's, and just finished dominating the light heavyweight ranks, and was about to steal the heavyweight crown from Holmes.. Holyfield was one of the very hottest talents out there, but had very fights in 1987 and even fewer against world class opposition. It wasn't until he made his heavyweight debut in 1988, at a time when Spinks was also declining that I would have picked Evander to take it... 1985 Spinks by narrow decision over 1987 Holyfield at cruiserweight.....
At cruiser Holyfield was an animal! Spinks was good, but Holyfield was part of the next generation of fighters. Holyfield was an excellent counterpuncher and stronger than Spinks. With Holyfield's solid jaw and quick reflexes Spinks would be unable to hurt Holyfield. Spinks would have to give up openings to get of his shots leaving the Spinks jinx on the mat for 10! Holyfield knocked out everyone he faced in 87. In 85' Spinks fought twice at light heavy knocking out fighters with 16-0 records before moving up and getting the gift win at heavyweight.
Holyfield. He shot that right hand out too quick at cruiserweight.. and there might be a left hook to follow it. Pin point accurate. Close but clear Holyfield decision.