I have mounted both the a/c compressor and alternator down low on my engine. I can see where the opti spark dist would interfere with this. I don't think I could have found enough room for the LT1's extra length over the short water pump setup, but for some builds that require the low mounting, the reverse flow and TPI might have been worth all the manifold fab work. Going from a manifold shown in Jerry's post to a functional manifold is quite a leap to make.