360 with 350-400hp, 6,000 RPM- what does it take?

No 360 is really better then another. The long blocks are all pretty much the same. Later LA 360 had Hyd roller cams. Some guys are getting good results out of 5.9L Magnums.

High 12s shouldnt be to hard. Get the compression up a good cam, intake and carb and some headers. Make sure you have enough gear.