Yes, you can use some of the 48re internals. The biggest single upgrade the 47 and 48 had over the 518 was the double wrap L&R band but that you cant use it in the 518. You can use every thing in front of the 48re L&R band in the 518 and some of the O/D parts, you can even make your 518 a lockup if wanted. The 48 has 5 plate front clutch, 6 pinion steel planetary carriers, much heavier drive shell, some of the cast iron parts are malleable iron instead of grey cast (about 3 times stronger). the 48re front annulus gear has double the teeth for the rear clutch disc drive splines.