Small block Water Pump

same shaft length between the 6/8 blade 'new style'
I know cause I switched with no issues.

Iyou need the deeper wp pulley and maybe even the newer crank pulley and alt brackets to move it outward some.

or...have your cast iron re man'd with an 8 blade impeller.

I'm not super wise on the early pulley configuration and what it would all take to switch to the newer pumps, I do know that the early A power steering cars had the pump bracket mounted to the driver side wp housing.