So my 73 Delta 88 has single exhaust and I want to have dual exhaust installed but running into issues because I am told the 455 engine on delta 88's has no available bolt on headers and or exhaust manifolds.... Can't be true but I can't find anything on line. The cars frame is setup for dual exhaust and the only thing I heard was a company called OPG who has a bolt on exhaust manifold to allow the duals to be installed...can anyone give me solid advice? The car is solid all original but it needs dual exhaust plus I have a current exhaust leak at the manifold

 

Have a 79 delta 88 with Bbo and headers installed, think the headers is more fit in a 73, look for more info in my Project thread on the last page and backward,its about engineswap,headers install and dual exhaust. Maybe it can help you a little.

 

Thornton sell manifolds for dual setup, I'm assuming yours is a 455.
You could also use the existing manifolds, lose the crossover and block off the hole on the r/h manifold.

 

Here is headers for your car, for b-body, you may have to adjust the rear pipe on the driverside, but i guess 73 delta 88 have a little bigger space than 79, and oilfilter and the connected for Oil filter need to be installed after headers, same as starter... In my case..

http://www.jegs.com/i/Hedman/500/58150/10002/-1

 

The 73 88 does not use the "Rear Steer" system thus the Thorton manifold is not necessary. I believe your existing manifolds are all thats needed and dual pipes can be run from them? The last dual exhaust 88 I saw was a 72 and the manifolds looked to be the same used in the A body cars. Someone chime in if I am mistaken about this...

 

Dual exhaust was a factory-available option on the D88 in the 1973 model year. Those cars used the X and Z exhaust manifolds. The W/Z manifolds (which are reproduced) will also work. Whoever told you manifolds don't exist doesn't know what they are talking about.