I found a service manual on eBay. It has turned out to be very useful. I finally found out what the difference between the BR320 and BR400. The BR320 has a 41mm bore -- the BR400 has a 46mm bore. The stroke is the same on both, giving a displacement of 44.9cc and 56.5cc. So, the only difference parts-wise is the cylinder and piston. I don't want to take the cylinder off to measure the bore, so I still don't know which I have, but now I know it won't make a difference.
From the manual I found that the spark plug wire screws into the coil pack. The original wire was too short, so I ordered some 5mm wire and easily replaced it. I found a good quality plug cap that I like. It screws onto the wire, but was for a 7mm wire, so I wrapped the end of the wire with tape to make a better fit. The plug socket is a proper brass and spring connector which makes a snug connection but is also easy to pull off. The standard coil spring with a spike into the side of the wire is too flimsy for my taste.
I ordered new Torqs screws to make up for the missing ones. I attached a picture of the new wire and cap. It's not much to show for, but basically I only need to repair the fuel tank and maybe find an orange engine cover. The tank on this particular model is bonded to the fan housing so replacing it would mean replacing both. Later blowers have these as two pieces. I'll probably just glue a patch over the crack and see how it goes. Otherwise, I'll look into plastic welding.