Was the block align honed ??
If so,you could probably just switch the bolts for studs,any difference may be minor enough that it wouldnt matter.Maybe Carl will post his opinion on this.Or just shell out the bucks to have studs installed and get the mains align honed.
Or for the little difference a windage tray would make,just run it "as is".
But if you want to do things 100 % correct and have your heart set on a windage tray,get the studs installed and have the mains align honed.
Or is an oil pan available for the 351 C that has a built in windage tray,like the Moroso one I have in my BBC ??