There are two dead giveaways as to H1R cases.
First, they all used roller bearings for the mains, and to locate the rollers, a number of set ring grooves were cut into the main bearing bores on the upper cases, so those racer cases would not only have the stock set ring groove, but 5 more, if I remember correctly.
The shift claw was also different for the H1R/H2R, it used an overshift stop claw on the top of the shift drum pins, as well as the actual pull lever on the bottom of the pins, and to get clearance for the claws, the area just behind them in the cases was cut away, milled down. This area is at the rear of the upper case, just above the starter stop bold boss, and was designed to catch slung oil from the primary gear on the clutch hub to the boss, and down into the starter shaft/gear inside the trans case area.
Them's the main diffs.