I recently installed a new set of protopline 180's on my 306.
I had to change pushrods also, so check the length.
The heads flow 5-10cfm more than the AFR 185's according to D&D motorsports and Texas Hot Rods. They come as cast and don't have the pretty CNC porting like the AFR head but the flow #'s are great. I was actually going to get the AFR heads but didn't want to wait an extra 3-4 weeks so I picked up the PTL heads with the higher rate spring package (up to .600 lift) for the same price as the standard AFR set up.
My 64 sedan ran a high of 12.92 @ 104-105 with a set of CNC power heads. the car is faster now but nthe shift point is up 300-400rpm to take advantage of the increased air flow, but I don't have any ET's yet. Hopefully this weekend if it quits raining.
hope this helps.