Had OEM engine guard (crash bar, highway bar, etc) on my 83 VT750 (sig pic) and they bolted to existing holes.
Although I never dropped it, it showed evidence of a hard spill while riding from PO and it did it's job - protected the left side of the engine/shifer, etc. Was a hard enough hit to bend it back far and dimple the exhaust pipe, and although it was mostly straightened back out, I suspect damage would have been much worse w/o it.
Don't think you can find aftermarket ones for these vintage Shadows, but the OEM ones show up occassionally eBay/CL (PRICEY).
Wish I had removed mine before I sold the bike as I'm sure I would have gotten the same price for the bike w/o them and could have easily sold them for $100-150!
Good luck in your search!
98 Shadow ACE 1100T (Tourer)
87 VT700 - sold.
83 VT750 - sold.