Gonna run a 9 lb pulley on a Radix. Which 5.7 Heads would be best to drop C.R. a bit?

 

Yeh the 5.7 heads should drop the CR but if you want a bigger drop in CR, go with 6.0 truck heads.

 

I would Get a Set of 6.0l heads as they have larger chambers to begin with
Most all the FI guys are going with them. I'm running a set of absolute speeds stage2 6.0l heads
Or you could find a set of used 5.7l heads and Drop your Comp just by adding them
or I would get a Water injection system

 

Yep, 6.0L #317 aluminum heads are biggest ( 72cc chambers ) and best for FI, next would be LS1 #241 heads ( 67cc chambers ). I THINK the CR on a 5.3L truck block goes down to 9:1 with #241 and 8.5:1 with #317.
Just to check, make sure there will be no valve side clearance issues with the larger LS1 valves, tho. Maybe post in the "Internal Engine" area, too.