You'll have to work on the crossmember or change it, the 518s don't have the tall mounting pad built in. TC should bolt right up. Output spline is same on both trannies. You are talking about 4x4 version of 518, correct?
You could make a u shaped piece and use your present crossmember, the 518s use totally different mounting system, you would need to get the bracket or mount that bolts to the tranny, mock the u shaped bracket with a piece of cardboard, any competant welding shop could make it.
I went out and measured a 207 208 extension housing off 727, they are 10 3/16" long. I have OD 4x4 housing but it's out of electronic governor unit 46RE, 96 and up. It is 10 13/16" long, 5/8" longer. Not sure if they changed the length when they dropped the hydraulic governed versions.don't think so but I been wrong once or twice before
The compounder that bolts to the back of the case in the 2 wheel drive version of 518, 46rh is about 3 or 4" longer than the 2 wheel drive long 727 extension that bolts to the back of the 727 case. I will show comparative pics shortly.
http://www.pbase.com/image/27313740 http://www.pbase.com/image/27313735 http://www.pbase.com/image/27313721 First pic is 727 and 518 case in side by side. second is 727 4x4 extension for 207,208,yada yada You can see difference in tranny mount pad but the ring the tc bolts to is same, the OD unit is 46re so it would have been used with drivers side drop tc. The 207 208 231 241 married 205 extension was in pass side drop application. Third pic is long truck 727 extension in side by side with 2 wheel drive compounder for 518, 618 46rh 47rh re. also included is the shorty used in divorced dodge tcs and some 2 wheel applications, in 2 wheel these always had 2 piece drive shafts. I don't know what the criteria was, I have seen club cabs 1/2 and 3/4 ton with one piece and 2 piece driveshafts, in other words both ways.
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