I bought new tires and wheels. I understand tire shops can mount them but the hubs don't fit on the balancing machines and some sort of adapters are required.

Looking at the various adapters and cones listed by parts suppliers I can't discern what I really need. I've seen cones sold based on mm. But what are they measuring? I've also seen an adapter. Is that all I need to fit on a spin balancer or what?

My wheels are MWS 6" x 15" with the hubs and lacing appropriate for a 1971 4.2.

 

You need a special adaptor or a copy. They are known as a Hoffman adaptor. You need an adaptor that matches the angle on the inside of the wheel so the wheel does not sit on the flat plate.

 

Here's a page linking mm and hub size. E-Types have the 52mm hub and are 73mm in diameter.

MWS

This page shows how the cones work

MWS

I got my cone adapters here

Wire Wheel Balancing Kit - Fosseway PerformanceFosseway Performance

I haven't actually used the cones because my rough balance on a bubble level worked so well.

HTH, Dave

 

I came across this https://mossmotoring.com/balancing-w...r-lock-wheels/ it says basically the same thing as the other links but explains it more clearly.
(IMHO)