The dbl roller chain is a basic hammer. Solid, reliable, quiet and well proven. The gear drives CAN be very noisy, but they do give you almost unlimited adjustment much easier than a chain. Some will fit behind a stock timing cover, but there have been problems with the guide buttons wearing a hole thu the cover. Pete Jackson gear drives are in particular quite noisy---sounds louder than an old supercharger! As for solid or hydraulic lifters....the solids will give you more rpm because they will not 'float', but they also require more fiddling to stay in adjustment. If you want all out power, and don't care how often you have to adjust valves, than solids are for you. If you want to DRIVE the car, spend as little time as possible under the hood, than go hydraulic. In a Cobra, almost any motor with decent power will give all the power you want. Remember that most '427 Cobras' actually came with 428's, just like the one in grandmas TBird (if she drove a Police Interceptor
). There is a reason Ford put more 428's in street cars than 427's! I would recommend the you go with a roller cam, either way. If you get an older block, there are plenty of conversion kits out there to put in a roller cam. The roller cams use much stronger profiles, for better all-around performance.