> 
> recent freebsd ISOs no longer work with memdisk.  if copied to a thumb
> drive it boots for either efi or bios.  might you clarify how you'd boil
> down the iso to distill a grub entry that works, preferably also for either
> efi or bios?

Yes, this makes sense (needing no ramdisk when booting from a thumb drive).

I do not have an ISO handy to look in it myself. Mount it (loopback) to
something like /mnt/tmp and go in there and see what it does. You should
be able to locate the kernel (in what would be [ROOT_FS]/boot for example).
You will find where all the startup scripts are; the "/" where they would
live is what your root filessytem will be for the GRUB entry. I am thinking
a GRUB1 entry that looks like one of these two:

title Slackware64 14.1 gflat
        root (hd0,0)
        kernel /vmlinuz-3.10.17_slackwareIN ro root=/dev/sda3 rhgb
title Slackware64 14.1 vr
        root (hd0,0)
        kernel /vmlinuz-3.10.17_slackwareIN ro root=/dev/sda2 rhgb

Points to the very first partition for finding all of its crap, then kicks
in that 3.10.17 kernel that I built, and uses /dev/sda2 as the root fs.

I love GRUB1. Simple and reliable if you do not need EFi.