Well, this was the first one I ever built:
The output valve is a 6V6GT although the only vacuum tube stuff I've done recently is a Nixie clock.
I guess I could fix the library so it accepts the 1284 and compiles, but can't test it on a physical board. Are you prepared to do the testing to check out the functionality ?
Is the 1284 the only board you've tried the example code on with the "MightyCore" ?
I've already had to make a fix it so it compiles with a recent IDE with the standard core. It looks like that could be a similar problem as that with the "miniCore". That I'll test myself.