its tough
the SOHC will need some modifications, the oil pan is wrong and in 99 it has a returnless style fuel rail
Your 94 transmission if its an auto will not work with the 99 computer, but the 94 computer can run that 99 SOHC engine
I have a friend Brett, he is a nutcase, he is a Ford guru and a mad scientist... believe me when I tell you this. Brett has a 94 Explorer sport, he installed a 2004 Ranger Edge SOHC 4.0L and 5 speed manual transmission into his 94 explorer sport... it is a TIGHT FIT, Brett also had to do alot of modifications to make it fit and work.. the 04 engine was modified with a OHV oil pan and pump, as well as a 97 SOHC intake manifold and fuel rail
he used the 94 computer to run the SOHC engine, believe it or not the only difference between a SOHC and an OHV as far as the computer is concerned is an additional camshaft position sensor on the valve cover of the SOHC engine.. Brett simply ignored this sensor and it runs just fine.
Brett still has some bugs to work out of his conversion, like I said it is a very tight fit and its slightly awkeward... the heater box must be modified, the exhaust wants to be in the frame and there are some other "tight" clearance area's
BUT IT RUNS LIKE A SCOLDED DOG
my 1988 is on 35" tires with a V8 and automatic
Brett's 94 Sport is on 33" tires with a 5 speed and a SOHC, both trucks are 4.10 gears... his truck keeps up with mine no problem... if we kep going he would likely catch me because the SOHC is so rev happy and he has a 5 speed....
Its a MONSTER conversion, but this is also a very difficult and detailed conversion, I would not attempt this if its your first rodeo
Wiring is tricky, details are tricky, even worse when you introduce an automatic transmission, FYI your 94 transmission will die a quick death behind the power of the SOHC
I have done several drivetrain conversion into these trucks, I wouldnt TOUCH the SOHC conversion .... I would instead do the V8 again, easier, in my case cheaper, and a MUCH better transmission