The 55 2nd. series had a V8 as an original option. The standard rams' horn manifolds should be a good fit, unless whatever kind of racing you're doing requires you to run full throttle all the time. Find a set of rams' horns for the 300 HP 327 with the 2 1/2 inch exhaust pipes and run a set of mid-1970's Cadillac mufflers with 2 1/2" pipes in and out. You'll have enough volume capacity for 1000 cubic inches, since one of those mufflers was used for the 500 Cad engine. Headers on street machines have two main functions- - - -raising under hood temperature at least 100 degrees, and burning spark plug wires. I've spent many hours on a dyno with small block engines and the only RPM where headers give a measurable power gain are well into the "speeding" or "public nuisance" RPM range. If you're just looking for eye candy for your ride, good luck- - - -no comment on that!
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!