New 66 Dart owner, wanting to swap /6

Hi all! I'm taking possession of a 1966 Dart GT with slant 6 motor on Sunday. The car is from a family member in another city, so I don't have a whole lot of information about it, other than it is an auto tranny and I believe it has power steering.

I am really wanting to put a 318 in there and have seen the notes regarding the various tweaks necessary such as throttle cable, oil filter 90 degree adapter, and the exhaust manifold issue.

I have found locally a 318 with 904 tranny from a 68 Coronet in a semi rebuild state and have a few questions.

My biggest question is the exhaust. I know about the TTI headers that work with this year dart on a 318, but that's a lot of money. I have also seen the spitfires made by Harold, but it seems like those may not be made anymore? It also says on the website that the spitfires don't work with power steering...is this still true?

I started looking into using a manifold, as I don't need this motor to make a LOT of power, and there are some options on eBay that say they work for a 66 Dart with a 273 motor. Would they also work for a 318?

Really just trying to find out what ALL my manifold/header options are for a 318 in a '66 with power steering.

In the event the car turns out to not have power steering, would buying headers or a manifold for a ps car still work?

Is there a specific radiator someone could link to that would for for this '68 318 motor in my dart?

Lastly, the goal for the car is to be around 225 horsepower. Is that achievable with using exhaust manifolds assuming I put on a new intake, 4 barrel, and a cam?

I'm excited about sharing the car with you guys and will post photos as soon as I get back from vegas in a week. Thanks!