Chris ,
I have a knife edge Diablo as well just like it that was gifted to me by 1/4 Away a member here when I turned 50 years old and I'll be 56 this year.
My understanding it was made in 1963 and being a knife edge (the curve in face of sight window) as bow face's you is something many want as a collector .
They stopped putting the knife edge on to save time on shaping as memory serves me correctly?
I asked Larry Hatfield that question myself and I "think" that was what he said?
Anyway here's mine with a few other Howatt's so enjoy that bow cause they don't make that style anymore and it has rosewood in it.By the way Diablo means "devil" cause it is a speed demon .