I went out and got a Haynes manual to fix the heater core in my 97 Avalon and the directions shown made it look so simple:

(IMG:http://gametrax.net/heatercore1.jpg)

The problem is, the metal chassis bar is in a different place on MY car:

(IMG:http://gametrax.net/heatercore2.jpg)

it comes right in front of the connection points, and one of the screws I need to get to is impossible to reach with that bar there. and it seems to be welded in place! I just can't figure this out. every other model year, the directions look so simple. I've looked at the directions for the 96 & 97 camry, the 97 lexis ES300, none of them have that chassis bar there :(

if anyone has a repair manual for the specific 95-97 Avalon model year, or knows something I don't, please help!

here's a picture so you can better see what I mean:

(IMG:http://gametrax.net/heatercore3.jpg)

so this ended up being easier than i was afraid of... the metal frame was only attached with bolts, two on top, two underneath, and one in the center. it was the two top bolts that were tough... it's a real tight space.