Which Serpentine pulley kit should I buy ?

Here is a link to March Performance. They say it’s a 3/4 inch difference between OE and FD. That’s a TON.

And, it’s a PITA to shim the pulleys that far. BTDT. You end up with weird spacers in weird places. And that’s a mile when using spacers.

It’s also possible your damper is somewhere between OE and an FD. Since my FD’s measure 1.4375 (which is 7/16) we can use 1.5 inches for easy math. According to March the OE damper would be 3/4 inch thinner than the FD, which means the OE damper is .750 thick, which is what my rickety memory thought it was.

I hope this helps you a maybe someone else who comes along later. Here’s the link...

March Performance - Serpentine Pulleys - Pulleys - Chrysler Small Block 318-340-360 - Chrysler