It should be relatively easy to fit any 4X5 Chromega colorhead on an older D chassis. If buying a used unit, you have to make sure everything is in good order, including the power supply and fan. And check the condition of the dichroic filters themselves. Dichroic filters don't fade; but over the long haul they do get dirty, or worse, some of the coating can spall off and make the filters ineffective.
But if seeking an unused or new colorhead instead, at that kind of expense, it might be wiser to acquire an entirely new enlarger, or at least a whole setup in excellent condition, which doesn't necessarily have to be an Omega.
Auto focus is something which can be ignored. It was pretty darn primitive back then anyway. D series chassis are remarkably simple. For decades, the tensioning system was nothing more than a pair of Acme window sash balancing springs.