zBuick, what year car are you working on? The later cars had the torque arm which makes trans change a little more difficult. The TH-350 is a bolt in with the correct tailshaft housing. The 200-4R will bea bunch more work but it is possible. Also, the stock turbo headers will not fit in an H-body without work. The hit the A-arm supports. I don't remember exactly but I think it was the collector region. Finally, yes, there are early low port heads and later high port heads. The headers are not the same. But, if the engine (4.1) holds water you absolutely have the later heads. The early heads won't fully support the headgasket so water fills the crankcase. Yep, did that. Ever seen water dripping from the front seal? Anyway, the H-body headers are very specific and I have not found a set yet that will fit unlesthey are H-body specific. I am also pretty darn sure nobody still makes an H-body V6 set of heades anymore. Ebay is your friend. But, for a mild build the stock manifolds will work fine. I think I still have a set that fit but I would have to check.