dunno if the MA and CG has the same cover layout but here's inside a CG cover
http://www.micra.org.uk/threads/pollymobiles-rebuild.35251/page-67#post-537731
the front port allows crankcase vapours to be sucked through the one-way PCV at the back into the inlet manifold during high vacuum. not suitable for oil drain.
the rear corner PCV breather port flows both ways:
during high vacuum, ambient air is sucked through the airbox PCV filter, through the cam cover, into the top of the cam area, down the timing chain passage, into the crankcase, back up the front pipe into the front port of the cam cover, past the PCV and into the inlet to burn the collected vapours.
during zero/+ve inlet pressure and +ve crankcase pressure from blowby (e.g.under high load), the excessive oily crankcase pressure flows out the open PCV breather port.
again dunno if the MA works the same as the CG but suggestions for where to plumb the oil drain are:
- dipstick (mentioned not possible)
- crankcase breather port at front of block with the cam cover front port blocked (so will lose some crankcase vacuum and vapour scavenging)
- drill a port into the side of the cam cover/upper portion of engine head to drain into the top of the engine with the camshafts etc
- drill a port into the top of the filler cap?