Its interesting you say that, because after I rebuilt a McIntosh MC250 for a friend of mine, I have been bitten by the McIntosh bug.....
Im setting my sights on a MC2100, or if I can wait, perhaps a MC2205......an MC2300 would be another choice......
But, I think a MC2100 would be an excellent place to start, there seems to be a lot around, and they seem to be one of the more accessible Macs ....
It seems to me the early ones like the MC250,2100, 2300, 2205 etc...all have the same basic design, in this design or topology, is the secret of the Mac sound......
I have been studying the Pre-amp circuits, and although I am not McIntosh expert, I do like the look of the C28 pre-amp......