classic motorcycle forum

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. 

Maybe people would have more luck finding stuff if they used the correct terminology, ie "Imperial" rather than "Whitworth".
Whitworth, as any fule no, is a threadform not a type of spanner.
These Imperial spanners are sold at UK swapmeets/autojumbles for a quid a time as there's no call for them. It's worth rooting through the boxes of tools just to get a range of spanners to keep with each bike.