[tcrist]

DV,
My headers (CR LTD) are actually stamped 302L & 302R on the header flange. To get the side pipes to line up if you are replacing a 302 with a 351 you should use different headers because of the deck hieght. CRII gets/got around it by selling different frame mount brackets that lower the 351 by around 3/4". This is according to Pete when I ordered the motor thru CR. I still had to remove material from the sidepipe cutout in the body to clear the sidepipe.
So what I see, in an older CR (as mine is a CR LTD) with the old type frame mount brackets, if you were replacing a 302 with a 351 and using the same headers, you would have to change to the new style motor mounts and brackets or your sidepipes will not clear the body.
In my case I changed to the new style brackets and still needed to modify the body anyway.
This really all depends on how much clearance was cut into the body in the first place.

Terry