The alternator conversion is listed in the 2nd gen forum in a couple places..... there is also the option of using a voltage regulator like what's on the 91 and earlier trucks... ... there is a difference in the regulator, depending on what alternator you use, too.....
Cruise control, other than a cable throttle lock, is not going to be possible without the ECM. Speedo can be worked around..... even made back to mechanical with a cable using an older speedo... ...
Personally, having cut the fenders on some, just make your own brackets to hold the ECM. It doesn't take much to move it up and forward and hold it. It's not very heavy..... and you can even move it to the firewall if you have too, with just a little rewiring.