Welcome to TC.
Thats a great first post! LOL
I think some of these guys are trying to bring you back to reality.
That small block engine with the cam choice needed to get 500hp will be essentially unstreetable.
Ignore what the slick salesman says in the ebay ad. Here is the actual catalog description for that particular cam:
Rough idle, needs good heads. Good upper midrange. Needs 3,500+ stall.
So you're going to need at least a 3500 stall convertor. You want to drive that on the street in Southern California?? I wouldn't. The powerband is listed as 2,600-6,400, this engine is not going to be happy unless its revving up high.
So, in other words, do you want to drive this car on the street, or are you building a race car???
For a street machine, you want low end and midrange torque. Stop looking at HP numbers. Instead of 500 hp, start dreaming about 500 ft-lbs of torque. I'd recommend you consider a big block swap. There truly is 'no replacement for displacement'. A budget 454 build can produce some serious numbers, and for about 1/2 the price of that skip white 383.
Check this article out. Its just one example of what a big block can do. And it is certainly streetable. They used a relatively mild 224/230 cam and 80's era iron TBI heads!
Displacing a true 461 ci thanks to a 0.030 overbore, the Demon 400hp 454 delivered more than advertised by producing 446 hp at 4,900 rpm and an impressive 542 lb-ft at just 3,600 rpm. Torque production from the big-block exceeded 500 lb-ft from 2,800 to 4,600 rpm. The Demon 454 belted out 490 lb-ft way down at 2,500 rpm and never produced less than 400 lb-ft. That, my friends, is why big-blocks rule. This motor would be equally at home in an RV, truck, or performance street machine and (if 450 hp and 542 lb-ft aren't enough) would make an excellent starting point for a more serious buildup.
Or how about this one? A 8:1 low compression wheezer that would run fine on regular unleaded. A simple ring & bearing rebuild with a summit cam and was still over 500 ft-lbs of torque.