That finished out nicely. It's a very unique setup. Are you able to run the furnace without the lower door open? That concerns me. It looks like a sure way to damage the unit. The manual seems to concur:
NOTICE: Do not operate unit with bottom (ash) door open.
Operating unit with ash door open can cause over-firing and damage
the unit, and will void any warranty.
NOTICE: Do not operate unit with bottom (ash) door open.
Operating unit with ash door open can cause over-firing and damage
the unit, and will void any warranty.