napa has core plugs.
here's the parts list.. I'd pay attention to number 3.
AR SBA110006030 ENGINE, SHORT Short Block, 1500, No Longer Serviced, Engine Assembies Include: Cylinder Block Assy., Crankshaft Assy., Camshaft Assy. & Piston & Rod Assy., Start Year: 01/01/
AR SBA110006040 ENGINE, SHORT Short Block, 1700, Engine Assembies Include: Cylinder Block Assy., Crankshaft Assy., Camshaft Assy. & Piston & Rod Assy., Start Year: 01/01/1979
1 1 Bare Block Assy., 1500, Start Year: 01/01/1979
1 1 SBA110106056 BLOCK Bare Block Assy., 1700 Includes: Ref. 2 thru 5, Start Year: 01/01/1979
2 3 SBA198466010 PLUG Plug 8.4mm , Start Year: 01/01/1979
3 3 SBA064100045 PLUG Plug, Start Year: 01/01/1979
4 1 SBA064100055 PLUG Plug, 55mm Dia, Start Year: 01/01/1979
5 1 SBA198516050 BEARING Bearing, Front, Main, Standard, Start Year: 01/01/1979
5 AR SBA198516460 BUSHING Bearing, Front, Main, .25mm or .010", NHNA Only, Start Year: 01/01/1979
5 AR SBA198516470 BEARING Bearing, Front, Main, 0.50mm or 0.20", NHNA Only, Start Year: 01/01/1979
6 2 SBA030501025 PIN, BALL DOWEL, M10 x 25 L, Pin, Start Year: 01/01/1979
7 2 SBA030500625 DOWEL DOWEL, Pin, M6 x 25, Start Year: 01/01/1979
8 1 SBA030300410 PIN Pin, M4 x 10, Start Year: 01/01/1979
9 1 SBA052300500 O-RING O-Ring, Start Year: 01/01/1979
10 1 SBA198736052 TUBE Drain, Start Year: 01/01/1979
11 1 SBA198416010 GAUGE Gauge, Start Year: 01/01/1979
12 1 SBA185246011 SENDER UNIT Sender, Oil, Start Year: 01/01/1979
13 5 SBA111136020 STUD Bolt, Start Year: 01/01/1979
14 1 SBA111136090 STUD Bolt, Start Year: 01/01/1979
15 6 SBA199376010 NUT Nut, Start Year: 01/01/1979
16 1 SBA199236260 RING Collar, Start Year: 01/01/1979
17 1 SBA110706090 PAN, ENGINE OIL Pan Assy., 1500, Start Year: 01/01/1979
17 1 SBA110706020 PAN Pan Assy., W/2WD, 1700, Start Year: 01/01/1979
18 1 87351909 GASKET Gasket , Start Year: 01/01/1979
18 1 87351909 GASKET Gasket , Start Year: 01/01/1979
19 14 86511315 WASHER WASHER, M8 x 16 x 1.6, Start Year: 01/01/1979
20 14 SBA011510820 SCREW, CAPTIVE WASHER SCREW, CAPTIVE WASHER, Hex, M8 x 20, G5, Start Year: 01/01/1979
21 1 412211 BOLT Screw, Cap, HH, CL8.8, M12 x 1.25 x 25, Start Year: 01/01/1979
22 1 SBA025100012 WASHER WASHER, M12, Seal, Start Year: 01/01/1979
23 1 SBA068118280 TUBE Tube, Start Year: 01/01/1979
24 1 SBA110706040 PAN Pan Assy., W/4WD, 1700, Start Year: 01/01/1979
here's the exploded diagram: