Headers VS Manifolds

I have a set of 340 TA ( HiPo) Manifolds commonly referred to as the "manifold header" they were mocked on the motor and do not fit the application..... they hit hard and bind the manual steering coupler on the drivers side and they dump directly over the torsion bar on the pass side..... they will be up for sale soon. 28635438 pass and 2863553 Drvr ..... They DO NOT fit a 66 with a /6 k, schumaker mounts and a 340 with a 727 behind, not even close!
When you say they will CHOKE the 340 what do you mean? nothing flows like a header I get that....but the 273 commando did pretty good out of the box and that is essentially the same LA motor as the 340 ....a lil bigger valves and point or two of increased compression true, but not that far off, they are pretty much matched HP for HP

273 Specs from a FABO forum called 273 specs

......................Charger/Commando................D/Dart
Horsepower...... 235 @ 5200 ......................275 @ N/A
Torque............ 280 @ 4000 ...........................N/A
Camshaft I .......... .425" .............................. .495"
E ....................... .425"............................... .505"
Duration ................248º.............................. . 284º
Overlap ..................46º .................................N/A
Carburetor..... 625 cfm AFB....................... 750 cfm Holley
Exhaust........ cast iron manifolds............... headers by Doug
Warranty........5 yr/50,000 miles...................... NONE

340 specs quote from ALLPar

The 340’s best power rating was 290 horsepower; even in 1973, it still managed 240-245 net horsepower.

ONLY 60 hp loss on the liberal side for not spending over $1200 is kinda acceptable and actually more like maybe 30 to 40 tops.....I can live with that.....

OK so the truck manifolds...... are they more "open" than the 273 manifolds and what modifications are required? even with manual steering there is NOT much room on either side , but it is pretty tight on the Drivers side do they feed straight out the back, then down? anyone have pics of them IN an early A?