any advice on where to buy /6 to 360 motor mount kit.t

Early a k frames are the same /6 or v8. Your cheapest bet is factory 273 mounts. I have ran a 360, 318 and currently run a 340 with unmodified 273 mounts. Some good bolts, washers and piece of 7/16 all thread is all that is needed to make them work.