Well, in the absence of anyone having done this before, I decided what the hell .
Ordered an oil return stub from eBay, 2 for £15 , the ones used for zvh conversions.
The helpful chap told me what side to drill and what tap I needed but had never done it to an engine block before.
I grabbed my cordless drill and 18mm HSS drill bit and got going drilling out the block

Started slowly using the spirit level as a guide

Actually cut quite nicely, on a slow and steady speed with plenty of WD40

Marked out the cross bore into the sump area

And then bored down



I need to run a die grinder along the sharp inside edges to relieve any potential stress points,
Then through the hot wash at work a few times and should be golden,
Oh, need to tap the hole to 1/2" bsp tho