Since you're already decided against pushrod OHV's, we'll take them off the table.
If you're going to go 2V, then the '02-'05 Ford Explorer/Mercury Mountaineer would be our best choice. PI heads/intake and aluminum block. No other Ford vehicle was equipped with an all aluminum 2V engine. If you do insist on using that F150, engine at the very least ensure it's of the PI head variety. The early non-PI headed engines were dud's as far as performance goes. PI heads and intake were found on Mustang's between '99-'04, Crown Vic's/Mercury Marquis/Lincoln Town Cars after '01. Trucks and Vans from '01-'04 got the heads, but you'll have to source the intake from another vehicle.
If you're going to go 4-Valve, then complete Cobra engines form '96-'01 are the ticket. The '99 & '01 being the more desirable than the '96-'98. An '03-'04 Cobra engine would be ideal, but it uses a cast iron block and supercharger...which aside from adding a considerable amount of power, also add a considerable amount of weight and cost to the overall engine package. If those aren't available, an, '03-'04 Mercury Marauder engine is virtually the same as the '99-'01 Cobra, but has the '03-'04 Cobra heads.
As stated previously, you could go with a Lincoln Mark VIII, Navigator, Aviator, etc 4-Valve engine as well, but take into account that all of these engines will require an upper intake swap for performance consideration. Which again, may, or may not add considerably to the cost depending on how inexpensively you're able to find the swap parts. A turnkey engine is always more desirable and less expensive in the long run IMO.
