Grant,
There are variations in the A series 4 synchro ones with breathers on too, there were a few different baffles used to minimise oil being thrown up into the breather.
The last of the non-breather ones had the same idler bearing size as these, and could be used instead. But as you can see there is little oilfeed provided to the idler bearing.
I would always use the breather one, on a 4 synchro box.
If you need any housings with breathers, come see me as I have a fair selection..

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DrMini- 1970 wasaMatic 1360, Mk1S crank, 86.6HP (ATW) =~125 @ crank, 45 Dellorto (38 chokes), RE282 sprint cam, 1.5 rockers, 11.0:1 C/R.
