Mechanical would be adequate if you're running carburettors, although a low-pressure electronic pump could be used instead.
If you're running EFI an electronic high-pressure pump is necessary as mechanical pump won't drive sufficient pressure to the fuel rail.
If you're running carburettors and your mechanical pump is good then I'd stic with it. If your mechanical pump is missing or fuk't then I'd not spend money buying another, replace with an electronic pump instead.[/Personal Opinion]