classic motorcycle forum

The hub and speedo drive both have marks which suggest that the speedo drive has spun at some point.
Do you have the missing parts to the speedo drive?

If you're sure the bearings are fully home, try adding a suitable washer under the centre of the speedo drive on the wheel spindle and then see if the wheel spins freely.
I've had a few do this over the years, and a spacer seems to free up the working of the speedo drive from being clamped by the wheel spindle.

Use a sliver of appropriately-sized shim stock?

I'm guessing if the OP has to ask the question then he hasn't got a lifter/decompressor of any kind fitted?

Worth bearing in mind that Renolds chain is crap these days and not a patch on how it used to be.

Don't know about in the colonies but in the UK prices for all bikes have slipped. A lot.
Where a good DBD34 could've made maybe £15/16K you'd get £9k on a good day. A7/10's were fetching £7-8k some years back but they'd struggle to achieve £5k now.
It's a harsh reality that those who like codger bikes are dying out, and their grieving families are dumping the bike collections onto an already flooded market, hence the price crash.
I reckon £2k would buy a top-notch Bantam now.

I wasn't contradicting you, just mentioning that in later years Meriden found a solution to that particular problem

Pre-war BSA (for instance) was part of a huge industrial conglomerate, and when odd-sized hexagon nuts turned up on BSA bikes it was because someone somewhere had ordered too much of a certain hex bar, and the accountants then wanted to make sure it was used.
People were more clever in those days; they just gone on with any repairs and didn't take to social media to complain that it took more than three spanners to work on their bikes.