To all you mechanics out there?

I bought a 1998 ford ranger 2.5 liter with a l4 motor. The only problem is it has a blown head gasket. Would it be possible to put a 4 liter v6 out of a 1998 ranger in without having to re wire everything and get a new computer?

Not possible. A fuel injected, OBD II, 6 cyl engine will not run at all with a 4 banger computer. And, the wiring harness will not attach to anything.
If you want the 6 popper, you NEED the transmission, entire wiring harness, radiator, entire exhaust system, and front springs, and fuel pump.

To save some money, why don't you just replace the head gasket?

You could probably change the "chip". The ROM that contains the engine operating instructions and the fuel profile.
You would also need to upgrade the suspension and drive train components to handle the added weight and power.
Why don't you just throw a head gasket at your 4 banger and be done with it? Trucks aren't made to race anyway.