1963 K10 Axle Swap - When did the rear perch width get wider?

[BFD305]

Hello All - Well I ventured out and picked up a '63 K10. Excited to get started. It is disassembled right now, so I figure its a good time to swap out the closed knuckle front and get some disc brakes too.

I found both front and rear assemblies from a '72 K10. I know the front will just bolt on, but not sure on the back.

What year did the spring perches get wider?

I have searched but have not gotten a definitive answer. Not a lot on these 60-66 K10's.

Thanks!