Solid “bolt” in place of valve stem!?!?

You aren't looking at the rim lock which stops the tyre sliding on the rim are you? It is fitted in the centre of the rim and is appears as a threaded stud with a lock nut.

Had 2 (I think.) from new on my '76 T140.

Makes changing tyres "Interesting" and not really needed nowadays IMO (Or in 76 TBH.).

Removing it will leave a hole in the rim obviously, and they're pretty heavy so will have a large effect on wheel balance.

of course and the main reason we should never do housework etc!

 I have Rim locks on both wheels of the 99.  I have had  3/4 punctures   all in the back wheel  . I managed to ride them all to a stop , one from   60 mph 2 up with camping gear at night raining on the MI,   Was not easy. Would I have managed with the  tyre coming off the rim and maybe  jamming in the swinging arm ?. Who knows . Hope I never find out. If they were of no use I doubt Norton would have fitted them. Another spoiler,  I have read that new pumps can wet sump just as fast as a reconned one. I suppose it all depends on the clearance between gear teeth and housing.

Only 3 options:

1) Ride regularly. We never had this issue when the bikes were used daily..... OR....

2) Fit a proper Full Flow On/Off tap in the feed to the engine - such as the Feked one attached. This MUST be fitted with a micro-switch to cut off the ignition as one day (as many people I know have) you WILL ride off forgetting about it.... OR...

3) Drain the oil tank after each blat, AND put the can containing the oil on the seat, as sooner or later you WILL ride off without putting the oil back in.

Any idea what the bore size of that feked Tap is?.

4) Get a Velocette-type anti-wet-sumping valve from Holland Norton Works. Tried and tested … (by me; usual disclaimer).

#H08 at https://www.hollandnortonworks.eu/en/exclusive-commando-parts

The rim lock is to stop the tyre slipping around the smooth chrome rim at low pressures used off road and then taking the inner tube with it and pulling the valve off. The tyre if its the right size and made properly even when the tube is fully deflated will not come off the rim but could drop inside the rim to the hollow for the spokes causing rapid deflation and you running on the rim not the tyre. If you look at modern WM profile alloy rims where the tyre bead sits they have serrations and the later still MT profile rims have an inner dam to stop the bead dropping in the spoke hollow for tubeless tyres.

If you fit bluetooth valve caps you can monitor the tyre pressures on the move and stop before they get too low so then you can throw the rim locks away. 

I rode a 16h with no rim lock in a time trial in the Czech Republic a couple of the years back The rear tyre moved on the rim ripping the valve off in the process with the inevitable consequence involving a hedge. On my model 18 I have newish tyres and have upped the PSI a bit. Fingers crossed!