So I'm replacing my evaporator and heater cores, and the evaporator core is just impossible to get in there. I had to cut it to get it out. Is it possible to remove the bottom of the plenum chamber, so that I could align the evap core through the firewall, then put the bottom back on?

Thanks.

Looks like I need to remove the entire plenum box. I found 2 nuts in the firewall in the engine compartment, one in the cab above the blower. Still not coming off. Anyone know where the others are?