There may have been 4-5 Mangusta built with 289HiPo's, but as a Mustang/Shelby guy I/we/you should know there were no 289s available after June 68, so the Euro/US thing is crap. I have a late car 8MA1244 and it has a 302 and unless you get down and dirty under the starter to see castings, see the front crank pulley or pull the heads one can't see the difference. 4 ways to ID a euro car; Km speedo, no rear markers (car in article is US car), and 2 tone tailights (which some owners now have changed)and some cars have a park lamp in the outer front HL ( but that is hard to see unless you turn on park lamps or see the flat beam.
As far as I understand my car (I have quite easily pulled the trans to change clutch BTW) there is no way the cast iron manifold would ever fit in there. When I purchased my car it had a 750Holley4160 with mech secondaries with the linkage on driver's side, it went like stink was real thirsty. left a trail of fumes and kept-up with cats, but I thought it was way too much carb, went to a 625 Holley 4150 vaccum secondaried with choke and lost a bit of bottom end but everything bolts fine, still plenty of fun to drive and a litle less thirsty, (a stock early Cat is still a few points better on gas on the highway though - ask Charlton
)my 2c but we are waaay off subject here.