Hi Creaky,
I think you have misunderstood me about how I do this. I have an M6 bolt passing through my timing disc, it is probably around 40mm long and the timing disc is fastened to this bolt using a washer either side of the disc and a nut tightened up against the back of the disc. The remaining portion of the shank of this bolt is what I screw in through the crank end feed seal, this sounds like a terrible thing to do, but as long as it is screwed in, rather than pushed, I have yet to damage any seals in this way. I suppose a larger, say M8 bolt could be used and any excess threads on the shank could be machined off, to leave a smooth length of 'rod' to push harmlessly through the seal. The engine can't be run like this, as you correctly assume, no oil will be pumped to the big end - although it would go just about everywhere else around you!
I just use this method for static timing of ignition and valves. It is also a very accurate way of finding, say, 38 deg BTDC, if you want to mark a crank position such as this on your alternator rotor, against a suitable fixed mark for strobing later on, after the feed quill bolt has been refitted!
B.W.