does anyone know or ever tried to swap an 81 4 cyl motor out of a mustang and put in a 305 chevy engine into it or does anyone have an idea of how hard this would be and if i could possibly get some information on how to do this thanks

I've seen it done, in fact I've seen many 4-cylinder Mustangs swapped to SB Chevy engines - apparently it was easier to swap in the Chevy than convert it to a Ford V8 - at least in the case of the Fox Mustang. I'm sure there's a bit of cutting and welding, but it can be done.

is all the wiring and computers going to need to be replaced with chevy ones?

not if you get a carbureted motor. they are simpler and often morepowerful, unless you get some real expensive fuel injection stuff...

is all the wiring and computers going to need to be replaced with chevy ones?

Yes.

You should probably use the Ford gauge sending units to ensure that the gauges read right. If you want to keep computer management intact, you will have to use a GM ECM, for that engine and weight of car (easier said than done. Blue Bowtie can tell you how to get a custom PROM for it), as well as the ECM's wiring harness and all necessary sensors (including EGO [or O2], MAP, BARO, temp, etc. The Ford ignition system uses a ballast resistor, this will have to be found and removed as the GM HEI doesn't use a ballast resistor (either block or resistance wire). You'll have to custom make a driveshaft (or rather have one made) for the application. Of course, there are the other things with engine swaps that need to be considered, such as custom mounts and things of that nature. There might be some things such as an alternator mod and whatnot to do - I am not that familiar with the Ford charging system so I can't tell you if the GM alternator will interface directly to it. There is a single-wire mod that can be performed to the GM alternator that makes it self-exciting so that you only have to run the one battery wire.

There's a bit of work to do, but if you want to do it, then I'm saluting you! I'd love to see another Mustang powered by Chevrolet. :)