The 44-year-old told the Birmingham Mail: "I remember when I first came in here, I spoke to Chelsea about Lukaku before we saw Christian. I knew about him and this club needed somebody to be that type of player.
"Obviously we couldn't afford that at that time and Christian came in. The rest is history, as they say. They're totally different players but the two of them are a threat.
"I would have tried to get Christian as well, probably. What would they have been like together? You really don't know, but they're two powerful lads."
Lukaku is likely to start for Everton tomorrow when the Toffees make the trip to Villa Park.