Hey imikus,imikus said:If you have the same rear end housing but just changed the gears, the fluid level should be the same. Minus the amount you need for friction modifier if need be. To be honest this is the first time I've heard of someone wanting too "flush" the rear-end. Did you change the gears for performance reasons or was the rear-end just plain worn out? As far as fluids go here's a couple of links that might help ya out.
http://www.amsoil.com/storefront/svg.aspx
http://www.royalpurple.com/prodsa/mgeara.html
http://www.neosyntheticoil.com/products_ge.html
http://www.motorcraft.com/products.do?item=15
http://www.castrol.com/castrol/multipleproductsection.do?categoryId=82915563&contentId=6032041
http://www.chevrontexacodelo.com/en/products/transmissionfluidgearoil/default.asp
http://www.76lubricants.com/NR/rdon...F54-AE8D-1644FB187E32/0/76TritonSynLubeEP.pdf
http://www.mobiloil.com/USA-English...bil_1_Fully_Synthetic_Gear_Lube_75W-90LS.aspx
All the oil listed above are good so I wouldn't get too hung up on brand name.