I think I should "qualify" statements about the exhaust, headers, stock 
manifolds, etc.  When I ran the '51 in stock class and they allowed headers, 
I first put on a set of  "Y" type headers and noticed a little difference 
over the tiny stock '51 manifolds but not nearly what I thought it would.

I later, over the years, made about three sets, even trying a four tube with 
the center port divided with a piece of metal welded to stick inside at the 
center of the center port.  When I started the car with those, I thought I 
had struck gold as it sounded way meaner than it ever had before.  
Unfortunately, it ran the same.  I tried a set with small pipes for the small 
valves the 232 had and a bigger set but nothing seemed to help much at all.  
I even ran the pipes back to about the rear tires and cut a foot off at a 
time and still could never tell much difference.

When I went to the R 2 engine I put it together with the biggest little 232 
headers just to get it running.   Later I made a bigger set to accomodate the 
larger valves, cubic inches, etc.  Again, I found it did not seem to help; 
therefore, my conclusion that there is not a whole lot to be gained on the 
exhaust side.  

I think headers will help some over the stock manifolds but for the dollars 
spent, I think you can gain more in other places.  If  you work on these 
"other places" (such as R 3 valves, cam, compression, gearing, etc.) and then 
have the $$ to go with headers, then I think it would be worthwhile.

I still have the stock manifolds on the '51 with the dual turbos but only 
because that was the simplist way to mount the turbos on the upside down 
manifolds.  I have made a set of headers for the Avanti (if I ever get time 
to finish it).

These have been my experiences and the opinions I have formed and may be 
entirely opposite of what some others think.