It sounds like the axle is too tight lengthwise and binding up the joints. Like the shaft might be too long.

I know your ride height is a little lower with the SBC, maybe the shaft sits different now. I would shim the axle housing up and away a little to try and gain some distance. Another option would be disassembling the CV axle and having the outer flange turned to allow the axle to fit a bit farther into the hub. Or machine the backside of the hub to do the same.