I used to “upgrade” those Brit cars at my shop; got 475hp out of them. Sweet ride, except for kidney pain from the Koni shocks.
Didn’t handle well - so much engine weight that slamming on the brakes could send car in a short side-wise loop. But I got mine to 180 mph before chickening out.
Ford engines 289/427 were withdrawn after too many factory shelbys and cobras were beaten at the track. But I see there is a new 2020 model out.