wave1957

I am trying to fit a 4L80E from an '05 Savanna van on an '04 LQ9 from a Silverado SS, but it does not fit. It has been suggested I need a 4L80E flexplate, but now my local Chevy dealer (and GMPP distributor) tells me there are 3 different 4L80E flexplates and they cannot tell me which will work... Help!!! Has anybody ever done such an installation? Can you tell me which flexplate will work, or how to find out? Although it is a Silverado SS engine, it is going into a '70 Impala...