I personally would put in a Cummins ISB with the appropriate RD option (from a delivery truck, etc) and go that route. 2-valves are lever actuated throttle. All 4-valve engines are drive by wire, however there is a cable going from the pedal to a spring that actuates an inexpensive throttle position sensor ($20 at your FLAPS) same setup on the Isuzu engine (Duramax) or a Navistar engine (Power Stroke)
If you want to keep it petrol, follow Jock's suggestion. A 383 stroker can be made for $2500 with great torque and plenty of top end by starting with a Vortec block and heads and an engine kit - plus you can build it to run on cheep pump gas.
