I have the manual setup. I don't think it is any harder to turn than the stock box but it takes some umph because of the 225 tires I am running.
My rattle problems are twofold. First, there is an intermediate shaft which connects the steering shaft which comes out of the bottom of the steering column to the rack. On my 68 this shaft is about 9 inches long. There are u-joints at each end of the intermediate shaft which slip over the shaft coming out of the rack and the steering column shaft and they are held tight by set screws. I have noticed these set screws tend to loosen every once in a while causing a rattle. Loctite was the solution here.
Second, there is a bearing in a cap that slips over the end of the steering column. The purpose of this bearing is to hold the shaft in the column steady. There should be no play between the bearing and the shaft but mine has a few thousands of an inch clearance. Not much but when that rattle transmits up through the column it creates a bit of a racket. This problem can be solved by spreading a thin coat of silicone sealant on the inside of the bearing before assembly.
Hope this helps.
68 Coupe, 5.0 EFI, 5sp