LS1 in '66 Nova?
https://ls1tech.com/forums/conversions-swaps/564367-67-chevy-ii-conversion.html
TKO Transmissions
They mostly focus on 5 speed conversions (hence the name), but they have some specs and retrofit info for T56's as well.
Hope that helps.
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https://ls1tech.com/forums/conversions-swaps/271478-chevy-2-headers.html
The Best V8 Stories One Small Block at Time
The may not have headers specifically for your application, but they have several LS1 models to chose from. They are anot all on their web page, you need to get the catalog. They are also very good to work with, I bought my headers from them in plain steel knowing we would have to modify them. They provided me with a box of scrap bends to work with for $20 and then after we had the mods done I sent them back and they Ceramic coated them for $115. And fast too, they had them back to me in less than a week.
I will warn you that sometimes the lady(s) that answer the phone are a little abrupt, but once you get to talking with the techs they are great to work with.
Pat





