The first seal you will install when rebuilding a Slant Six is the rear main seal.

There are two main seal types available, one is the "rope seal" and the other is a new rubber type lip seal.
The rope seal must be "packed" into the receiver groove in the block and the main seal cap. A piece of 2 3/4 inch round pipe makes a good tool for packing the seal into the grooves and the cap can be installed over this tool to check seal alignment. Any excess rope fibers must be trimmed away from the surface where the seal cap meets the block.

Since most of todays gasket sets come with the rubber lip seal, we will show how that type is installed. All the related gaskets, their installation / positions are the same for both types of main seals.
Note that the lower main seal cap holds the main seal as well as two cap to block, black rubber side seals, shaped like an "L". The lip type main seal is directional and must be installed in it's groove so the flat side of the lip is facing to the inside of the engine. The angled or sloped side faces outward. It is a good idea to do a trial assembly with the cap / main seal prior to installing the crankshaft. Check to be sure the seal halfs line-up properly and "paint mark" the sides to help with proper reinstallation later.

One "trick" I use with these hard rubber lip type main seals is to offset the two halfs in the grooves somewhat. This helps the seal halfs "self align" by overlapping into the mating groove, this also prevents the parting lines of the main seal and the cap from being on the same plane. The side "L" seals are installed using a small amount of silicon sealer, this not only helps them seal but also helps you slip the assembly into place. This view of the rear main seal cap shows the side that faces outward. When the cap is installed correctly, you can see the heads of the main seal cap bolts from the outside of the engine. remember to apply a small amount of oil or assembly lube on the seal's lip and crank journal surface before the final installation.

Once the main seal / cap is in place, I always clean the protruding "L" tab ends and mating engine block surface completely, then glue these tabs down with weather strip adhesive or rubber cement. This prevents the tab from slipping out from under the cork oil pan rail gasket. Be sure to allow yourself time to let the glue dry prior to installing the oil pan.

With the main seal installed and the tab glue drying, now it is time to install the timing chain cover. Always check for dimpled bolt holes and burrs. Deburr and straighten the cover as needed. Install a new front seal and then the large rubber seal which runs across the bottom of the cover. (Pull the slender rubber "pegs" through the small locating holes, those small holes you deburred, right?) Some small dabs a silicon sealer, needle nose pliers and a rotating / stretching action get the pegs through the holes easily. One trick I use to install the timing chain cover is to drill-out the dowel pin location holes on the cover and then install the cover with all the bolts loose, then I install the front damper (or damper hub) to center the front seal lip on the hub surface. With extra clearance in the dowel locating holes, the cover / seal assembly floats and self centers, then just tighten the bolts. This should always be done if the crank's main line has been align honed.

The front and the back is "buttoned-up", now it is time to do the oil pan install. Once again. do a trial fit, pan to block, no pan rail gaskets, just to be sure everything is flat and all the holes line up. (that's right, check each pan bolt hole and file-out any holes riding close to an edge or overlapping.) Check your oil pickup tube placement to the oil pan floor at this time. Try not to knock loose the glued down "L" tabs while you do all this checking.

Put a dab of sealer under the front rubber blocks of the timing cover bottom seal, right where the cover meets the block and seal. place dabs of sealer in the glued down tabs at the rear. Run a small bead of sealer along each block rail and lay the two oil pan rail gaskets on top. The rail gaskets overlap the rubber pieces to the pan side as shown. install all the pan bolts and just draw them down for full contact but don't tighten. Allow the sealer to "firm-up" then come back and do a final tightening, starting from the center of the pan rails and working outward. Do not over tighten . (watch to see if the gasket material starts to buldge out from under the bolt areas).
DD