I've been mulling over similar ideas lately... I don't know how much longer I can hold out before a 911 lands in my driveway. There's a tatty yellow '70t locally that I could pick up if I wanted it... solid, mostly rust free but a bit tired. Probably ~10-12k.
But for 12k, I figure I should be able to get an 84-86 Carrera that needs paint, and then backdate it. I *really* like the 3.2/915 combo, but I would probably be just as happy with an SC if I got a good deal on one.
I think a backdated SC/Carrera has the PERFECT look: