I know this thread is old, but I found it searching for an answer to the same exact problem. I have heard varying stories, but some say that non-factory A/C sometimes had the straight expansion valve. Others say that they are from another AMC product, and towards the end they were running out of parts and just used whatever was lying around that they could make work.
There are two issues...the straight through Expansion Valve is an O-Ring connection, while the 90 degree is a flare. The second is hose routing. I was looking into converting from straight to 90 degree, and while possible it would take a ton of work (rework of the heads on the hoses as well as cut / weld different bends into the evaporator.
But I found a solution.
Old Air Products -
oldairproducts.comPart Number 25-8731.
Hope this helps someone! It took me a few weeks of research to find this and figure it out.