I have a number of authentic haggis recipes from the early 1600's. the common ingredient is oatmeal. two recipes have no meat, one includes mince, one liver, one has various innards. Though all the recipes call for boiling in a sheeps stomach they mention a pudding cloth can be used, or it can be baked in a pan in the oven.

Odd that the one using the innerds is the only one that seems to have survived.