Seems you have the excact engine I do....Mine came from a `72 model car (prev owner installed it in my 69 convert.). the YX is a factory 400 ci V8 2bbl rated 200 hp automatic engine....mine was installed w a th350 though, I also have a 4 bbl 650 holley on it...the 7J2 heads are what I removed , got some help/input from a couple of sources here and on PY board...I bought a set of 5C heads on EBay for $150...lesser known but good flowing heads w the bigger valves (most people use the more known 4X, but they usually sell for more), had them checked out for cracks,checked the CC`s on them ,they were at 95 cc, had them milled to 88CC , and should now give approx. 9.2-9.3 CR...runs good on "plus" gas ,no need for premium , and I also went to 1.65 rockers from the 1.5 ,and kept the orig cam...car runs great now... You may also check your rear axle, mine is set up for cruising rather than racing and I have the least "rubber burning" ratio....but still squeels out...I have the 2.56 rear and like it since I mostly drive on hwy.I also added a B&M shift kit for better shifting. Now it gives me 14 mpg on hwy at 70 , about 9 in town. No idea on my hp now but should be around 270-280 ,my best guess
