Engine IDnumber heads

Your casting number is for the '68 to '75 5 freeze plug RG 225 block. There should be a number faintly stamped on the passenger's side front of the block, facing up, under the alternator bracket where the head meets the block. It is kind of hard to locate until you know where to look. This will typically give more precise information. If the block has been decked in the past though, this stamped number may have been removed in the process.

The drool tubes have gaskets that are easy to change (FEL-PRO ES12794). As mentioned when putting new plugs in remove their crush washers. Make sure to torque the plugs to 30 ftlbs.

Many people like to run NGK plugs (ZFR5N 3459) gapped at 0.035" in their slants. Total timing will depend on the exact distributor you have, since the governors and vacuum advance pods can vary quite a bit. There should be a metal tab on the distributor with a part number stamped on it, but taking it apart and seeing what is stamped on the vacuum advance pod arm and governor will tell the true story. Conservatively you should be able to set it at 5* BTDC (low idle) as a starting place.