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Didn't the original listing say it came with 1 1/4"
Alpinestars often came with 1 1/4".
https://www.sjscycles.co.uk/stems/alpinestars-alloy-quill-stem-w-vertical-cable-routing-160-mm-plus5-deg-black/As it happens I've got a 1989 MS Racing (which is an ancestor of your frame). Although I'm sure that takes a 1" stem/hs. I should dig it out. One of these:
http://fcdn.mtbr.com/attachments/vintage-retro-classic/440491d1237312406-ms-racing-alpinestars-cr-1.jpg but only f&f and repainted.
At first glance I thought that Syncros one was a ahead stem with quill adaptor. Looks fine, more period correct for the build yes?