Thanks for this! Exactly what I wanted, as the busybox I flashed, and could not change without a new kernel, doesn't support bz2 or lzma only gzip.
So just to be clear it should be good if I...
'adb push'd the zip to my /sdcard/
'adb reboot recovery' into TWRP that I flashed before
selected install, and chose the ROM zip
Cleared my Dalvik and cache areas
Rebooted into the bootloader
'fastboot flash boot boot.img' while in the folder where I expanded the ROM zip
Finally rebooted, and am done?
adb seems to connect me as root now, and /system can be written to...so I think it worked! Unfortunately Stericson was the same version of busybox I already had. Will have to search around for that other copy. But at least I can replace it now!