JFTR, it might be easier (and safer!) to use a simulated magnetic tape image that simh can create on-the-fly from data file(s), so that it's RSTS/E itself which is loading and saving the file onto the file system. You won't need any extra tools to what you already have.
In simh:
sim> att ts -rf DOS11 yahtze.tsk yahtze.sco
In RSTS/E's DCL:
$ mount/over=id ms0:
$ copy ms0:yahtze.* [G,M]
$ dismount/unload ms0:
where [G,M] is the PPN on disk where you want to store the files at.
Disclaimer: I typed the above from memory, as I don't have a running system handy ATM -- so please consider those just as an idea (not an exact recipe!), and adjust accordingly, if I unintentionally messed something up ;-)
HTH