Little info that I know is that the older first generation TH-400's (you have a 425 but they are pretty much identical only different haha" the torque converters were interchangable and I doubt that GM changed that. This is back when GM cared. Here is some links for information about your transmission and some upgrades you might consider while doing the coversion, especially the Switch Pitch portion, I have had a few older Eldo's and it makes a world of difference at both spectrums power/economy.
http://www.remaker.com/caddy/survival.html "Scroll down to the SWP portion"
http://www.california.com/%7Eeagle/SWITCH.html
http://www.bdub.net/tranny/index.html
Hope all goes well and let us know, I have thought about this type of conversion before.
Mike
1995 Suburban K2500 6.5TD 3.73's Innercooled, Updated cooling, Banks 3" exhaust no gizzards in the kittie. Pyro/Boost/Trans temp. Transgo HD valvebody kit.
2002 2500HD, CC, LB, 4X4,California Truck, Federal Emissions Front pipe, Plugged recirculator, modified air box(Per Kennedy's page) 6" RCD lift, 35" tires.