Hi Don,

From time to time there have been ambitious folks that have made a run of adapters like what you describe. I've seen them built for installing an 88-92 truck computer into older vets, to replace the 86-89 Vette computer with a 90-91 model, and even a few to upgrade the 88-91 trucks. Vans never get any love.

You might find an adapter but here's my thought: None of the wires to control the 4L80E are present in your harness. Even with the adapter you still need to add them. So maybe the easiest answer is to locate a complete harness from a 4L80E equipped van? I know from working with a fleet of school buses since 2003 that the one ton cutaway chassis vans usully came with 350 / 4L80E. If you could find one used then you'd get all the parts you need for your swap.

Barring that, you can buy a used ecm and a couple of connectors and make a harness. It's something you can do in the house or garage, sitting at a table or bench in comfort. You don't need the same number ECM as what's in your van because the ECM plugs for many of the older TBI vehicles are the same. I just searched Ebay for GM TBI ECM and came up with a pile of computers (there's a 1227746 for $20) and the red and blue connectors for the 1227727 (one seller has them listed for $12.95 with free shipping). I usually make a chart to help keep track of the changes and to note anything that's different such as when GM has added or deleted circuits of features over the years. It can take a few hours to build a harness but it does save a bunch of time when you're ready to install the ecm.