OK, I've got one of those magnetic pendulum protractor thingies and mounted it on the frame in a couple of places to see how the frame sat in the garage. It was just about perfectly level. Then I mounted it on the top of the valve cover, and it measured about 4 1/2" degrees. Since I just got done with a complete resto, all the engine and tranny mounts are new...however, I do have a Toyota gearbox conversion, and those mounts are different then original. I imagine that Herman from HVDA got it pretty close to original, so your 5 degree estimate is probably pretty close.
I know when I put the header from Moss on my car, they must not have taken that into consideration, as the header pointed down a few degrees with the engine and trans installed. What a pain it the butt that was getting the angle right. It took a couple of trips to work using the acetylene torch even though I tried to be very careful making a cardboard template. You may have to fine tune as I did once everything is in the car.
Edit: I know I have a TR3, but the frame to engine relationship <span style="font-weight: bold">should</span> be the same as the TR4. Of course, that may be a wild assumption! :laugh: