You guys are going about this the right way. Install the cam, mock up the engine, and check your lifter preload. Don't assume that 7.400" is right, because more often than not it will be too short to get lifter preload back to the stock dimension. You will be light on preload, you'll get more valvetrain noise, and you'll be running a much heavier lifter because of all the extra oil inside it (earlier valve float). I had an LS6 cam, and it measured .029" smaller than the LS1 on the base circle. I've also have a Comp XER that was .040 smaller, and my current LPE cam is .050" smaller. Don't assume that there's a standard for aftermarket cams, because there isn't. Because most of the LSx cam lobes are already as tall as will fit through the cam journals, the only dimension that the cam grinders have to play with is the base circle, so that's how they change the lobe lift. Most LSx engines have .060" or more preload stock.
FYI, it's impossible to accurately recreate valvetrain geometry without taking the eventual lifter preload into account. If you use soft "checker" springs and adjustable pushrods, you won't get any preload while you're checking, and if you use normal valve springs and an empty lifter, you'll get lifter preload, but the lifter plunger will sink as soon as you start lifting the valve off the seat, and it will really sink as pressure builds when the cam goes over the nose. Incorrect results again. IMO, the safest thing is to take good measurements and get the preload back to where it should be. Take notes on changes in valve length, milling, gasket thickness, pushrod length, and stock lifter preload.