I was going to ask this same question awhile back. I think early 87 540's 550's etc would be the PL1770C (tolex chainsaw) I think the PL probably stood for ProLine but thats what the 87 price list shows. Then late 87ish to 89 or so would be the rectangle Tolex with the white piping (RG550LC), then they started with the Plastic molded cases M100C and you had your choice of the tolex or plastic as you bought them separately. The USA Customs first came with the RG550LC but had a badge that said USA Custom, Then the M150C molded case. The molded cases changed some over the years from Charcoal fur or Black fur and the badging from prestige deluxe or professional deluxe, etc..thats where I need the help to determine which is which.
Here is a link to the 87 price list showing the case: http://www.ibanezrules.com/catalogs/.../2_Jun/p02.jpg