I finished building the second Hercules Model G Westwood wheel this weekend. It's another copy of the original spoke pattern: 32 spoke cross 3. The spokes are DT Swiss straight gauge stainless steel. The nipples are 14mm brass DT Swiss. I once again incorporated nipple washers at the rim and spoke washers at the hub.
The rim is an Avro 26 x 1 1/2. This is yes another copy from the original size. The main difference, so far as I can tell, is that the originals use a little heavier (probably better) steel, and the originals had a black paint stripe down the center at the spoke holes. I did not paint these rims because I've never been happy with my results anytime I try to paint over smooth plating. I've opted to run them as plain, plated rims.
The purist's answer for replacing spokes is to use the exact same part, at least when you can't use the originals. I have no aversion to straight gauge spokes as an option over double butted. The difference in weight does not concern me, particularly on this bicycle, which is already pretty heavy. Where I differ with original is in using stainless steel. I don't mind galvanized spokes, but I also like the corrosion resistance offered by stainless. It helps keep rust and pitting off of the spoke structure. It also resists that nasty state when corrosion gets into the spoke threads and freezes the nipple into place, preventing adjustment. My compromise is to use spokes the same basic size and shape as the originals, but with stainless steel as a more practical measure.
The front hub appears to be original. It's a thick hub with a metal filler cap with the letter "D" stamped into it. If I had to guess, I would say that means it's a Dunlop hub. Many people are familiar with Dunlop tires. In fact, they were a mainstay of the high quality bicycle parts market for decades. They made some of the best bicycle tires on the planet. However, not many people are aware of Dunlop's contribution to other parts. Many of the vintage English bicycle rims, bear a Dunlop seal.
Whether Dunlop actually produced them, or simply licensed their marque out, I am unsure. However, it is not uncommon to find Dunlop rims. That said, I have never seen a Dunlop oil filler hub before. It's plain steel with plating. The plating shows some wear, but that's perfectly common on a bicycle approaching 80 years old.