Gibson sg special
If you should not like the P-90's there are a bunch of humbucker replacements with apprpriate dimensions so that you'll not need to route/ruine your axe. You could choose a Duncan custom shop soapbar stack, which delivers the P-90 tone without the hum. Then, there are the duncan vintage, custom and seymourized mini humbuckers, which are cool (I like especially the vintage one, not too hot and well balanced). Surely Dimarzio has pups in that dimensions, like the virtual P-90 and the mini humbucker. If you should not like the Gibson P-90's but still want singlecoils, then Fralin and Harmonic Design have some really good sounding P-90's. The difference is that they don't sound too midy, but opener, say better balanced tone, but still P-90.
I have put a pair of Fralins in my Gibson SG Classic, and it sounds like heaven!