If you're ok with boost, then Bone stock 351w + on3 turbo kit might be the cheapest way to go.
500whp should be no problem.
I'm OK with boost, what size turbo and how much boost can be safely run on a stock long block and pump gas?
Seems to me that your best bet is a high compression solid lift 302 that you rev the snot out of.
If I go this way, what would maximum safe revs be for a Ford crank and rods?
You will also need to verify adequate bearing clearance. Those large diameter journals require more clearance than most are accustomed to using.
Will make a note of that...
If he was closer, I'd make him a deal on a 400 block I had worked on in the late 80's ... Boss 408.
Would have loved to take you up on that. Still think it would be a cool build, even if only to say, you did it.
I'd look into what guys are doing with stock 5.4L engines and a turbo on the fuel you plan to use.
These would be run of the mill, 5.4L 3V truck engines. Any recommendation for a turbo on pump gas, over here that would be 95 octane at the coast? And might I ask why you specifically mention the 5.4L, over the 4.6L, is it just because you start of with a larger capacity?