Stuart,
According to the EW spares list, the front and rear chains are 1/2x3/16”, but it does not say the number of links.
The clutch sprocket is 22 teeth.
The shock absorber sprocket is called out as 41 teeth, 1/2x3/16”. An alternate sprocket is given of 38 teeth, but no chain size specified. Since there is only the one clutch sprocket, it is presumed to also be 1/2x3/16”.
For the final transmission sprocket you have a choice of 17T (solo), 15T (combination) and 18T.
Just one final sprocket was offered, 57 teeth, 1/2x3/16” (solo or combination). I think this is welded to the brake drum (it is on the later 350cc machine), so it is a repair item.
In 1928, the EW was called the A28, and a combined spares list for the five 1928 350cc models exists.
The same part number clutch sprocket is listed.
The same part number 41T shock absorber sprocket is listed, but not the 38T.
The same part number final transmission sprockets are available, with the addition of a 14T (solo) and a 16T.
The same part number rear sprocket is listed.
The same part number chains are listed, and this time they give the number of links. The front is 1/2x3/16”, 80 link. The rear is 1/2x3/16”, 112 link.
In addition a 5/8x1/4 chain is listed for the B28, a colonial version of the A28. So there is also a new 47T, 5/8x1/4” rear sprocket listed for that, but oddly, they omitted to list the compatible final output sprockets! Or else the two new final output sprockets of 14T and 16T are miss-identified as to the applicable model. Since this is a multi-model spares list, they used a letter code to indicate what combination of models a part would fit. The primary chain arrangements were the same as the A28 and so EW.
But for the EW it is clear, 1/2x3/16” front and rear, and the 1928 list gives the number of links. However it probably goes without saying that you should get chains a little longer and shorten them to suit your sprocket combinations!
-Doug