> Confirmed broken with external artwork. This was due to a change by hap on 30/7/2017.
> One of the artwork guys would need to adjust the lay file.
Yup, I broke it, and promptly fixed them. The fixes have been forwarded to Stiletto a month ago, but he hasn't had the time yet(or forgot?) to update the MESS artwork page.
Fixed .lay files here: http://tsk-tsk.net/net/temp/hh_extartwork_fixes.zip
They are compatible with older MAME versions too.