Here's a link to the parts drawing for the pump and related parts, including the pickup screen. It's inside the transmission at the bottom, labeled 49 in the drawing. Torque Converter Transmission Oil Pump & Related Parts
And here's a link to the parts drawing for the transmission case. Torque Converter Transmission Case & Related Parts
I haven't been into one, but it looks like the access cover on the bottom, labeled 3 in the second drawing, might give you access to the pickup screen from the bottom.