For what it's worth, for decades I drove a 2.56 behind my 455. And honestly the engine could have worked great with much taller gears and a lockup convertor. Granted I've had EFI forever so I've had good engine control. But remember that the modern 3800 engines, which are half the size, do great at 70MPH and 2000RPM going up fairly steep portions of highway. So a 455 pushing an A-body down the highway takes SO little effort for our huge torque-monsters. After enough time with the 2.56 gears I wished I could have gotten some 2.29 gears or even put a GearVendors before my 2.56. If I hadn't been pushing so much nitrous, I would have gone for a 200-4R with lockup in front of my 2.56's. The engine now sits in our '73 LeSabre with 2.73 rearend & 28.5" tires- and even with the 5000# car (which often tows a car trailer so total load is around 9,000#-10,000#) the tall 2.73 gears are no problem at all for long highway cruises. In other words don't worry about a 0.64 top gear with 3.42's (=2.19), our big V8's are barely working on the highway and detonation shouldn't be an issue. Especially with a manual transmission where your converter isn't slipping at low RPM's. And if you are climbing the Rocky Mountains and worried about detonation, you can always drop to 4th gear. Just one guy's (unpopular) perspective... -Bob C.