Used Mark 40H gear case.  We have rebuilt this gear case with new bearings, seals, water pump cartridge, L ring, prop shaft bearing carrier and cone nut.  We also have a new Mark 55H length drive shaft with extended crank shaft splines that allow the drive shaft to be cut down 3/8" for use on a Mark 40H.  We can do it for you if you like.  You can leave it at the current length for use with a Mark 55H tower if desired.  The gears and the prop shaft are used. I would say the gears have about 45% life left in them and the prop shaft in side is very good but the out side is only fair.  This is an less expensive way to install a rebuilt gear case on your D engine as our rebuilt 55H gear case sell for about $200 more.