For what it's worth I put a KC SBF 427 with a Dart aluminum block in my cobra. Reasons: 1) Roush is BIG - the good is a very good "we'll fix your problem" record and dealers are close by (everywhere?). The concern is that they have many "certified" builders vs. KC who does it all in his shop - I assumed this meant more control by Keith over the quality/who's building it, etc.part. 2) Price: got essentially the same quality parts plus upgraded to the DART aluminum block and it still cost less (including shipping). While the downside of a KC engine is that you have to deal with Arkansas instead of a local dealer I have to say that I had a shipping problem that damaged the
oil pan and carb and with no questions asked KC immediately shipped replacement parts at KC's cost. The engine has run flawlessly so far (only 3000 miles and not racing) but it is definitely strong. I ordered a slightly de-tuned version of the KC 580HP motor. KC measured it at 554 HP at 6000. After installation I put it on a chassis dyno (inertial dyno in 4th gear - 140mph max) and got ~425HP so the KC dyno number seems to be reasonably good. By the way, torgue was something just north of 580. Given that this motor is lighter than the original 289 and ~12% more powerful than the original FEs I'm guessing Carol would have given his eye teeth for this motor in '65. Not only does the 554 HP keep the power to weight ratio ~the same as the original (slightly heavier SPF still behaves like an original) you can drive it to breakfast or in heavy traffic with no problem. By the way, I get 16 mpg (freeway) with a carb. <{:>))