I treat the pre-commando engine exactly the same way as the Commando one, and block up the holes between timing side and crankside (circled in red).
Additionally, I drill a new hole lower down (circled in green), and block up the original oil drain hole.
I like the lower hole, as I see noticeably less air in the oil that gets returned to the tank - I assume it is getting whipped up far less.
I have done two 650ss Dommies like this, and am very pleased with the results.
The first, I fitted one of Comstock's sump plug reed breathers, and for comparison the second engine I fitted a reed valve on the back of the crankcase (same position as the Combat)
I remove the rotary breather plate and spring that engage with the end of the camshaft, and block up the breather hole in the crankcase.
The result is a leak free bike, whose breathing is excellent.
The performance of these reed breathers are noticeably better than our MK3 Commando - to this we have fitted one of Comstock's sump plug reed breathers and have blocked up the factory standard breather union on the back of the timing side 'ear'.
However, the standard holes between timing side and crankside are still there.
Increasing the size of the cavity under the piston acts as a damper (or cushion) which lessens the effectiveness of the reed.
In fact, I would assume that at high rpm it doesn't resonate/pulse like it is designed to do, rendering it effective only as a pressure relief valve at higher revs.
Don't get me wrong, it is still effective (and an absolute godsend for clearing a wet-sumped crankcase) - it is just not as efficient as the setup where the holes to the timing side are blocked.