Dad restoring '66 Mustang...

Most of the guys in here will tell you those are the guys to go to for the I6 200.

fuzzy, you might want to talk to the BIG BLUE FUZZYCLOSET MONSTER, aka 65stanger. Fritz is in the middle of a major restomod on Sally, including some baseline work on her 200 ci six-in-a-row. If I remember correctly, he's been doing some research on exactly this topic - although I've been teasing him that the best upgrade to the 200 includes the word "Cleveland"

Seriously, talk to 65stanger - like I said he's been doing some research; including talking to others who have "been there, done that".

There was a kid (yeah, I mean kid, like 16-17 yrs old) who hung around the Classics Forums and who's been working on his 200-powered ('66? '67?) and has done some stuff which was published in Mustang Illustrated back when Jeff Ford was the editor. I can't remember his Screen Name and haven't heard or seen him in a while though......