Changing the number of file headers on an RSX volume

So I'm working on this RSX11M+ system here and while working I ran myself out of file headers. Using the HOME /MXF command I was able to increase the number of headers, but only up to 4090. or so. Trying to go to 4100 gave me an error saying there were not enough system blocks or something. Currently I have 830 headers, but that's not enough in the long term. The volume has 541,944 blocks total, with 150655 in use. This is a system I generated on a smaller disk, then copied to the pdp11, then backed up with BRU MU0:=DU0: then restored to a larger blank disk. I guess the question is can I extend the number of blocks without having to re-init the system disk? I suppose I could flatten it by taking the system down to single user (shutdown, then p to start with the volume dismounted, mount the volume /for, then BRU mu0:=du0:), then format the volume with a really big assed MXF value, then restoring the tape, but would that flatten the volume info? Or do I need to just man up, put a second ESDI drive on this monster, copy the files to the second drive then format the first (big) volume right, copy the files with PIP, and do a VMR again to write the boot block? Or is there a better way to backup and restore the volume without doing an image backup using /for? Been a long time since I've done this stuff. Thanks! C