318 block drain plug

Everything @cudamark said is spot on. You will be much better off pulling the motor to do the job if you have the capability to do it yourself. If you can pull it and do it yourself, drain the oil also before you pull it. When you get it out, stand it up on its back and pour the water jackets full of white vinegar. You can pop out one of the freeze plugs in the front of the motor, or one of the ones on the heads to pour it in. Let it sit a few days, then drain it all out, pop all the freeze plugs out and pressure wash every hole out. You will be amazed at all the crap that will come out. It will be a little bit of work, but it won' cost very much. A new set of brass freeze plugs, 2 gallons of vinegar, 2 gallons of antifreeze is it. That is, if you don't do like I did and let that same job turn into a new set of TTI headers, swap out the 904 for a 727, swap out the 7 1/4 for an 8 3/4, new driveshaft, new exhaust.....lol. Good luck to you on the repair.
:thumbsup: