How much does it cost to rebuild a Slant 6

The leaks on the oil filter side look to be a combination of the valve cover gasket and the spark plug tube gaskets. When you pull the spark plugs on the older head, there are aluminum tubes that go into the head and surround the plugs; these tubes just pul out and there are small gaskets around each one; easy to buy and replace. Same for the valve coer gasket.

There looks to be some sealer around the timing cover to pan gasket area. Not uncommon for leaks there. You pretty much need to jack or pull the engine up a few inches to work on the pan gasket. Timing cover gasket can be done in the car. I'd replace the timing chain if I did the timing cover gasket; will help performance very noticeably.

Looks like coolant on the k-member edge.