Hi,
Manhattan is a Davis model N which is a 3/4 sized machine. The needles are called Davis long, Boye 10, 1x2 depending on who makes them. The 3/4 sized shuttle and bobbin are somewhat scarce. The full sized Davis shuttle is common and much easier to find. The needles are just shy of 2". The 3/4 shuttle is also a bit under 2". The bobbin is 1-1/4" long. I'd check the online auction sites and ask around various chat groups for parts.
Jon