This one may give you a head start. The base Program is set up like a unison doubler, but you can (manually) adjust Pitch A & B to say, 3rds & 5ths. The A HotKnob shifts both pitches together.
https://patchstorage.com/adt-quantize-doubletrack/
For high gain ‘internally’, try swapping out Mod Delay for any one of the distortion algorithms. I’m sure I’ve built something similar before, but I didn’t find any with a quick scan of PatchStorage.
