The oil filter was an option for most years on the 6. Since yours lacks a filter, if it is a '59, it is most likely a 235. The '50 261 has a slightly different oiling system, with a filter being standard on them. They require the filter, or at least bypass plumbing in order to oil properly.
Adding a filter is not hard to do. There's a few ways you can do it. One would be to find an original canister filter, usually AC or Fram, with the appropriate hoses to connect it. The feed line comes from the same port as the pressure gauge, the return is about at the center of the block on the driver's side, and should have a 1/8 NPT plug in it. Another way would be to use a Trans-Dapt or similar brand filter relocater that uses a modern spin on style filter. This would a bit cheaper, as the filters tend to run less. However, if you go that route, you will need to add a restrictor in the return line to prevent pressure loss. You could also use a Frantz filter, which uses TP for the filter media. Those hook up the same as the original bypass filter.
To identify your engine, there's a few numbers on the block that will Id it. One is the block casting number, found toward the front of the engine on the passenger side, near the motor mount. This will get at least the range, as the same casting numbers could be used for multiple years. Another is the casting date, which is located on the passenger side near the starter. The casting date is usually about 2-3 weeks from the asembly date. The last number is the engine serail number. This is the one that's stamped on the flat pad next to the distributor. That number will tell hich plant the engine came from, and what vehicle model it was installed in originally. It may also tell what transmission and clutch option it was equiped with.
