Boyd
If the brass restrictor plate is missing from your engine block then YES you'll need to purchase and install a new one. Normally people leave them in, unless the motor has been hot tanked.
New ones are not available from Ford, but a forum member "Marlin Jack" manufactures and sells them, you'll find them on eBay, his eBay member name is neon fiddler.
351C brass restrictor on eBay
-G
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