My dad has an old m550ab made by westernfield which i did some research into it and its a mossberg according to this guy on youtube Western Field 12 Gauge Shotgun - Mossberg 550 New Life
Also when after disassembling mine and seeing a video of someone disassembling a mossberg 500 all his parts are exactly the same looking. So my main question here is would i beable to purchase a mossberg 500 16" barrel and a new stock and pump and use the parts on this gun?

Also while i am here the receiver is scratched to hell and back is there anyway i can remove the old finish and give it a nice black or silver look. What materials would i need to do this?

Yes, the Western Field 550 was a "house brand" shotgun that Mossberg made.  It is, for all intents and purposes, a Mossberg 500 and 500 parts should interchange freely (there has been some evolution of the 500 over the years).  Yes, current 500 barrels will fit the 550.
Buttstocks should interchange within the same gauge, although I think that wood and plastic buttstocks have attachment screws of different lengths.
There is variation in forend length.  You most likely have a "long" action slide and will need a "long" forend (go to www.havlinsales.com , select Modern Shotgun Parts from the menu on the left side, and then scroll down a little for a picture and descriptions).

For a receiver refinish, Brownells' Alumahyde has worked quite well for me!