This might vary as I'm using a 1998 T100 into a 1991 4runner so your mileage may vary.

Up until now all the swaps I've read note that you can use either alternator with some modification to get them to fit the bracket, however if you used the 3.4L donor alternator you needed to do some soldering to rewire the harness.

Yesterday I was at this step and going back and forth between the alternators. I did not want to cut and resolder the harness because the gauges were different and I wanted to keep everything as clean as possible. After going back and forth I resigned myself to having to use the 3.4L alternator and was going to cut the harness. But first I wanted to switch the brushes from the 3.0 alternator because I just swapped those recently.

As I opened the back plate of the alternators I realized that the brushes were the same.

3.0L



3.4L


So I took the brushes out of each one and sure enough the 3.0l brushes were much longer than the 3.4l brushes.

But I noticed something else these two alternators looked exactly the same minus the plugs, what's more they are in exactly the same location... and they look like they can be swapped.

Here's the 3.4L with the plug and the heatsink removed.


Here's the heatsink and plug by itself.


Here's the old 3.0L heatsink and plug swapped to the 3.4L alternator


I've not got the swap running yet, but I don't immediately see a problem, the alternators look exactly the same, except for the mounting points. I will update when the swap is running if I let all the magic smoke out.

 

never remembered to update this until now, but yes I haven't had a problem with this swap for about a year now. So this is a viable swap on the heat sink and connectors between alternators. I'm not sure if the alternators vary over the years, but at least from 1998 T100 swapped into a 1991 4runner this did work.