The surface between the timing chain cover and the plate that cover the oil pump gears has a specific "tolerance" or space that is required to allow the oil pump gears to perform properly. The gasket that goes between these two surfaces is called a tolerance gasket. I have personally had my cover off numerous times to stop a leak. I have noticed a difference in thicknesses of that particular gasket, between various companies, that make the timing chain cover gasket set. The reason I say all this is... I think sanding the surfaces may have done more harm than good. The covers are around $235-$250 range and the "improved cover" that you mentioned has been talked about here in the Forum before but I can't recall the exact price...I do know that it about floored me!
Don't used any sealant compounds on this gasket either... may gum up the journals in the pump. Sorry if I am the bearer of bad news... don't feel bad....I have lived with my leak for 1.5 years and fixed it....and 6 months later I found a hairline crack in my cover!
Others may disagree with what I have said... this is what I have been told when going thru my dilemma...
78 Wagoneer "River Beast"
Dana 44's w/ 3.54's (soon to be 4.88's)
7" SOA conversion
4" Skyjacker Softride
3" Trailmaster Bodylift
33x12.50's on 15x10's
(soon 38.5x14.50's on 12's)
My FSJ site: http://www.geocities.com/~spazz4life
"Where there's a hill...there's a way!"