Yup, it's not a 420, I have one in my truck, it's original, and it's a '50. 1st gear isn't synchro'd in the SM420, but the rest are, as you probably know. If you don't mind double clutching the crashbox you have is ok and probably stronger than the 420 but it will be a pain to drive on the street, loud, and is hardly worth anything- A real SM420 is probably worth 3 times as much. The pre-SM420 chevy 4speeds had the same ratios I think as the 420s but were not sychronised in 2nd-4th gears. The cases look almost the same in both of them but the shifter on the crashbox has a reverse lockout lever and the shifter on the SM420 doesn't. I suggest you either get your money back or use the tranny you have if you are not going to drive on the road and are good at double clutching. Have fun with your cruiser.
