Depends what you want to do with the car..If you want to go fast in a straight line then buy it..BUT if you want to be able to really drive the car & drive it for extended lengths of time then stick with your plan..Having had a similar motor 700hp 429/460 in the Green Mach I purchased from a member here the wow factor wore off real quick..The car handled for shit..you couldn't take more than a half hour or so behind the wheel was just a dog to drive..No fun at all..Pulled that motor & c6 & sold it this past summer..
I have always believed in a more balanced refined approach to my builds since I really like to be able to DRIVE MY CARS..I want them them to handle..take long trips with ease..still have the power required when I stomp the pedal..I was going to do a 408 stroker too..but the more I thought about it the more research I did I came to the conclusion why do that when I could build a nice user friendly streetable 351c with 380-420 hp more than enough for the street..I also knew that my other 351cj q-code car was awsome to drive had plenty of power handled great..was a fun balnced package I could drive for hours on end..In doing my research I came across an article that confirmed everything I had known..So I changed my plan no 408 stroker..Faux 351c CJ build 4r70w tranny..all the upgraded modern suspension components..
Heres a cut & paste from that article some food for thought:
Building a 351C based stroker motor is contrary to the spirit of the 351C. It returns to the excesses that Ford designed the 351C to leave behind. I'm convinced if a high performance street, sports car or road racing enthusiast wants a 500 bhp engine the standard displacement 351 is a better choice than a stroker displacing 383, 393 or 408 cubic inches. A smaller motor builds power more gradually as the engine speed rises, it doesn't make 400+ foot/pounds of torque abruptly at 2000 rpm like a stroker does, the power is delivered in a manner that is easier for the average driver to control, or to put it another way, in a manner making it harder for the tires to loose adhesion. Choosing balanced performance over brute force is my recommendation. Build a 400 to 450 horsepower 351C, a task which is not difficult or exorbitantly expensive; keep the power delivery controllable; equip the car with the lightest wheels, the best tires, performance gears, lightweight drivetrain parts (drive shaft and axles), the best shocks and the best brakes you can afford; lower the chassis; and lighten the vehicle to improve the power to weight ratio. Truly going fast on street tires is not a matter of how big or powerful the motor is, but how well balanced the package is.