Except on the RX’s. The RX01 was 128 byte sectors and the later ones 256 and a odd interleaving strategy. However, the boot block and the rest of the file systems (both UNIX and RT at least) just aggregated the smaller (logical) sectors together to make a 512 byte one.
Indeed, I was less than precise -- the key is that the SW treats them everything as being in 512 byte 'hunks' no matter the underlying physical formatting/interleaving actually is.
The point is that if you Paul is trying to move data from the two systems, just treat the device as a serial byte stream of 512 byte blocks on both sides and you you be fine. That means if using dd, add conv=sync to fill any write buffer to a complete multiple of 512.