[Tom Goldman]

66 Impalla rear will fit the 150 nicely,its within 3/8" of stock width.
Just weld on the spring pads.
I've got a '57 150 in the shop right now with this rear, altho it's got a LS 3 Vette engine in front of it!
Just keep in mind 12 bolt gear ratio availability for those little motors.
10 bolt rears have a better availability of very low ratios, and will certainly hold up behind a 265 or 283.