I would place him in the top 10 for sure

its very difficult to build a top 10 cos you have fighters like jack dempsay who were practically super middleweights so how would he cope against a monster of a heavyweight like lennox

but here goes in no particular order

muhammad ali
joe frazier
george foreman
lennox lewis
evander holyfield
joe louis
jack johnson
mike tyson
sonny liston
ernie shavers

i expect some ear ache for leaving rocky marciano out