Hi Coupster,
Voice of experience here.
DON'T get one of these from Ford
Whichever engine size you select, go with a builder who stands behind their product, not a junk & garbage supplier with no warrany such as Ford
Their defective parts and assembly cost me an extra $2800 after 812 miles of gentle street use. Ford's response: "no warranty".
Having made that point, I now have 6000 miles on my 521 and have enjoyed them all
since the engine was repaired
Nothing sounds better than the idle, except maybe the sound when you do get to open the secondaries a bit!
Tom