Another Ossa MAR basket case project  and daft question's but I'm guessing that hole is not meant to be there??? If so why drill a hole? Does it need to be welded or can I bung it ?? I've got 2 engine's 1 with broken con rod and this one which is almost there but with a hole in the crank case. Just my luck. Your thoughts appreciated ?

It's a non-standard hole made for the ignition cables to protect them a lot better than the standard hole which is underneath. If the cables come out the hole underneath, they tend to get squashed between the bashplate and the engine casings

That makes sense now. Thanks feetupfun?

Yes, got the same hole on my MAR

This forward and up hole does work well.

From experience doing this mod, you should use a low output heat gun or hair drier to warm the protective sheath over the wires as you feed them through this hole, and as you route them when installing the stator.  Heat will soften but not melt the sheath if done with low heat and allow the wire harness to easily follow its new route and placement.

as the wires are routed up the frames right side down tube, be aware to keep them away from the exhaust heat, and still remain protected from abrasion.

Once everything is assembled, a small amount of sealant will seal up where the wires pass thru the hole.  Regarding the bottom hole from original, you can use an original grommet and seal the previous wire openings, or add a small fuel filter to avoid water entry and keep dirt out while letting it breathe.