I would probably not do head gaskets again on my 3.0L. 3.4L for me. I think another issue you have to deal with is the oil pan and sump. Tacoma 3.4L's have a different suspension set up so the sump is at the opposite end of the engine, (don't remember which is which). If you get a 3.4L from a T100 I think it will fit ok though. Other people can verify this better probably.

1997 T100 extracab, 3.4L, 5-speed, 169K, 4x4. Love the truck, never buy anything but toyota, I tried it once, most miserable six months of my life.