Question for the engine builders!

While it is acheivable on the smaller cubic inches you will need to run some special parts (ported heads and intake) and higher rpms. The large cube motor may make it a little easier to reach your goal and keep it maintenance friendly. I have a customers 345ci motor that makes well over 670HP and goes 9.20 @ 145+ @ 3150lbs but it is a 8800rpm motor with a lot of money it in, 100% race car.

Regardless plan on a aftermarket race block if you can, it will hold near what ever you through at it now and in the future. Yes the 69-74 factory 351W blocks are known to be the stronger blocks, 69-70 use a 9.48" deck height, 71+ is 9.503" but your builder should already know that.

I think the budget will make it hard to do the chassis and the motor, fuel system, drivetrain etc correctly but depending on what you find as a roller it may be possible. 500hp from a big cubic inch Windor done right is no problem. Is this a street car? Does it have to run on pump gas? I assume this will be a automatic car, c4 maybe?

Rick got you runnin in the right direction as a general rule of thumb the bigger the cubic inch the more power with the same supporting cast. So the 351 windsor gets the nod here, not just from a cube point of view but a much stronger piece without having to buy a race block. The stock Windsor crank and rods are very strong pieces but I think I see a stroker kit in your future. Get a nice 393 or 408 kit, and look to top it off with atleast 185 or 200 cc heads and a camshaft of 240/250 @ .050 with about .600 inches and a Vic. Jr intake. That should get you near your goal on HP and still remain fairly streetable to cruise around town if you get the itch. Check out the AFR site for the Motorsport 393 they played with.