it's too bad all of the $42 hacks start at D000, meaning all of the RAM address are cutoff...
however:
http://www.thirdgen.org/techboard/di...o-winaldl.html
confirm:
0052 is the BPW MSB
0053 is the BPW LSB
so what i would do:
change D4E7(will show as 04E7 in the TP hex editor) to 00 52
change D4E9(04E9) to 00 53
^assuming those aren't reversed anyways
then change a working $42 ADX and outright modify the PROM ID value instead of making a new one. just call it BPW, we'll deal with scaling later if it's correct. don't do any of that LSB first stuff since it's not necessary since we are able to modify the stream. save the BIN so the checksum updates and test.
that's what i would do.