I am still having problems. Can you try this image - it should be non-banked and work with the serial port. It has your HLDRBIOS code in the cpmldr. When I try it it reads the cpmldr, displays the sign on and jumps to block 0x40 and then complains of a BDOS Err, Perm. like it can't find the directory. I assume I don't need to modify the boot rom for no holes as it is only in the picture to load the cpmldr from track 0 and that appears to work?
Thanks in advance - I don't see why this should not just work now.