57 Exhaust manifold - Dual vs. Single Exhaust? Help!

Well, I purchased what was supposed to be a left side NOS 57-58 exhaust manifold for a dual exhaust; well it isn't. The one on my car is about 9.5" longer coming back to the exhaust pipe. Can anyone confirm that in fact this is correct for a 57-58 single exhaust? There is a number 23 cast in middle and then a casting number in the back of 1186505-2. If it is, is this extra length of pipe the only difference? Is sure appears to be the same otherwise, from what I can see...

It sure looks like this is in fact a left NOS 57-58 manifold, which is still quite valuable, but not what I need. I am trying to confirm so that I can decide whether to 1)resell it and buy the correct one (if I can find one) or 2)if the only difference is the extra 9.5" length, install it and install an extension onto the exhaust.

You're help would be appreciated!

Lance, It is a left side but not a dual exhaust. It's a single.

I beleave that the manifold you have falls in the 59" range I think the on you are looking for looks like this one wich is

a #1171945. This is the manifold we bought for our 58 with a single exaust.