Shoulda used Forth. It'd be fairly easy to go from assembler to an ultra bare bones Forth, and that could be built up to work like Pascal, until it looks like Pascal-written-backwards. Then write the compiler in that, and the translation and bootstrap would be trivial.
My first thought as well, but in 1969 Forth was still busy being born. Based on the notes here[1], many of the core concepts of a modern Forth like defining words and the structure of the dictionary were being actively hammered out.
