At the very least, MacTCP supports System 6 and the 68000; Open Transport is incompatible with both. (I seem to recall there's a version of OT you can use with

At the very least, MacTCP supports System 6 and the 68000; Open Transport is incompatible with both. (I seem to recall there's a version of OT you can use with System 7 Pro, a.k.a. System 7.1.1.)