Yes, I have a drawing. There are a few things you should know. First, Bob Lamour in Canada can supply these to anyone who is interested. I am using one of his on the racer I am currently building. These are done to print, so if the print doesn't meet what your needs are, make your own.
Second, this adaptor was designed for Lightnings and Flashes, so it must use a 1/4" chain, which is generally stronger than the 5/8" chain. If you wish to make one for a different chain you would have to check the dimensions.
Third, you may want to use a different material, like 7075. The ones I have are made from 6061. These have worked well for high hp Comets but based on Greg Brillus having problems with his twin sprocket adaptors cracking I would take some care in choosing the material and the design. My adaptors are solid, which I think is a key to prevent cracking, so I would not machine any additional holes.
Finally, the adaptor can be machined to match the thread on the new sprocket bolts if you choose to. I have done this on mine.
I use AN bolts for the hub to adaptor and I have found for the Comet that 5 bolts are sufficient.
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I have one or two done to print if someone has a need. Otherwise, the drawing is the best starting place.
Bob Larmour does a nice job. This is one that he anodized. The holes were threaded also for the Suzuki RM sprocket.
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The part no. is at the top. It is 452 with the number of teeth (48) added.
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The sprockets are 7075 and are available in tooth sizes from 30T to 74T. The part number is 452, which can be seen in the photo.
David