i really can't see much of a issue with the pressure or heat...
the oil pressure that a motor works at is next to nothing..
the alloy & O-rings will handle 200 deg with out knowing they
are doing it...
The side pipe with the pnumatic snap lock fittings will be gone
holes pluged with 1/8" BSPT plugs... only use the 2 top fitting
holes with the pipe tails in them... if lucky they may have a JIS
thread in them that hydrulic fittings will screw into...
Maybe I should start with a bit of 100mm alloy bar & spend a few hours
on the lathe...
but that tanks a lot cheaper than a bit of 7075 solid alloy bar... will try the tank first...
For what it is worth.. The top looks to be a separate piece held on with screws, that would need to be oil tight at pressure. If you only use the top two connections, what is to stop the oil short cutting between the connections? It would be better to come in at the top and out at the bottom. The other top connection could be used as a vent.
I suspect it will be fairly thin gauge material, and would be susceptible stone punctures.