Good luck, it is a big wide alt. It will fit.
You also need the gm wiring plug to the back, I am pretty sure NAPA sells it or any junk yard.
I am sure you can do it.
You don't need a plug for a "one wire." ('s why they CALL it a "one wire.") By the way, you can convert ANY GM integral 10/12SI to "one wire" just by putting the correct regulator in it.