Is the disk image independent from the disk hardware? I’d assume that different disks may have different block sizes etc, so the disk type may be important.
A reasonable thought, but no, other than efficiency. It's just an array of bytes exposed to the OS.
The good news is that all the DEC systems used 512 byte fixed blocks (Nothing like the funky Prime, Apollo or Alto tricks of putting some of the file system metadata into the physical disk format -- if you ever wondered why some of the original SCSI controllers supported a 1072 byte block size - it was for Domain/Aegis - 1024 block + 48 byte meta data].
The target system is LSX, a cut-down version of V6 designed to run on the LSI-11.
Everything should be able to be simulated using is 512-byte blocks.
There are very few system utilities in the standard build (no mount for example). The second floppy is permanently mounted at boot time. I’m interested in making source file floppies on my modern system to use on the LSX, so I want to be able to create an image file from a source folder tree.
You'll have to check the docs, but I thought Heinz supported the RK05 [RKV11 controller]. That will give you 2.5M of 'raw' disk blocks, instead of floppy. Open it raw, and use it like mag tape. If you don't have a coming format, you can create something and then use dd(1) on the LSI-11 from the RKV11 -- a little clumsy but as a bootstrap, it should work fine. The RL11 and RK711 controllers (RL01/02, RK07 disk) came later to the PDP-11 (post 11/34 and 11/60). I think there was an RLV1[12] at some point, but I don't think DEC even made an RKV71[12] -- however, I'm not up on late-generation PDP-11 lore and they would have been much later than LSX so driver support is doubtful.
Good luck,
Clem