I did have a set of shorty Hedman Hedders #78070 painted like $179 from Summit IIRC
on a stock 383 in a 68 RR, BUT they helped the performance some, how much I'm not 100% sure,
I'm sure more HP/TQ than the stock HP manifolds, far less reversion,
better flow if nothing else would bump it maybe 10% on a stock type combo "free flowing"
BUT so did the 770cfm Street Avenger, RPM Intake,
K&N Filter & 1.6 ratio Crane Ductile Iron adj. rockers,
hotter ignition & coil, low ohm resistance wires etc.
The Hedman Shorty hedders I had, they have 1-3/4" short tubes like 20" long & 2.5" collectors
But;
I had a 3" Flowmasters American thunder Series 50 exhaust system,
I made my own head pipes out of scrap 3" mandrel bent tubing, the 2.5 collector rings {barely big enough}
I encapsulated a fastener on each side the pipe was too really big on the 2.5" openings,
I had to have one bolt from the top, welded captured nuts on the other 2 to have easy access,
from underneath, I could access my starter & the wires pretty well {IIRC}...
It won't work with a Unisteer Rack & pinion thou, that's long story, low car no room for long tubes,
I made a different custom set of hedders, 1-3/4" stepped to 1-7/8"
with Flowmasters scavenger 1-7/8" merge 4-2-1 to 3" collectors,
when I went to a stroker combo latter, that car went 8.58 @ 156 on a 300 shot N20
9.77 @ 135 N/A thru the mufflers @ 3520#'s on old drag radials
that custom hedder went up & to the back to the fire wall, than down with the collectors,
tried to make them equal length tuned pipes, what a bitch that was...
kind of like the S/S Iron manifold from 63-64, was my pattern sort-of...
it had pretty goo starter clearance then...
sorry got off track a little...LOL
Anyway they/Hedman shorty headers fit really well IIRC
no dinging anything on the 383 in the RR IIRC, it's been like 10 years ago now,
I had new style Dakota mini starter too, always a bitch in most any Mopar BB...
It was a low deck B-block too, the hedders don't hug the block quite as tight as the RB blocks do...
Sorry never had any shorty's on a RB block...
IIRC the only issue was the drag link or pitman arm {I can't remember which}
was close, I had to do a little minor quarter shape flat spot ding for clearances,
in the 3" head pipes I custom made... Doooh
they even fit the angle plug Eddy RPM heads,
just for shits & giggles I checked...
Sorry no photos of the custom swept back style hedders either...
good luck