Same dimensions and bolt holes, and will fit all L-6 engines, but if it's important to you, they don't all say the same thing on the top. Most are "Nissan OHC", yours is obviously "Turbo" and don't the 240s say something else. No biggie. I've always wondered if there was a way to cast, weld or machine in different words/numbers. Guess there would be if I threw enough $$ at it.
I bet it could reduce heat dissapation somewhat, althought not significantly. Any time you polish anything, it reduces the surface area. You are essentially removing the ridges and protrusions that the rough metal has. Like what has more surface area per sq. mile, the great plains or the rocky mts. It is the same kind of thing. Greater surface area means greater heat dissapation. But I doubt it could really make that much difference, especially for the valve cover!
Yes, JR...I saw a "Rhino" Ferrari 250 GTO body conversion in Tejas and the owner had the words milled off the valve cover...he bought some cast letters and epoxied
them on..."Ferrari"...of course...looked good...don't know what it cost him but milling ain't cheap...a Dremel tool would work...if you have lotsa time!!!... )