Years ago bootstrapping 4.1BSD on a vax730 (a very mini variant of the 11/780) all I had was single disk removable rl02 type platters. And had to do a sequence of

  dd seek= 

Commands to split a 1200 bpi tape read ona larger machine nto chunks, write to the pack as a raw bits to read off, and reassemble as a boot structure to install from.