Yes, that is a crankshaft seal, they are inexpensive and I would replace it especially if the balancer has any groove in it. Also be mindful of a high volume or high pressure oil pump, if you are not doing any head work ( valve stem seals) the increased oil may result in smoking/oil consumption. The 3970014 block should give you 100 years of more service.
1957 Chevrolet 5700 LCF 283 SM420 2 speed rear, 1955 IH 300U T/A, 1978 Corvette 350 auto, 1978 Yamaha DT175, 1999 Harley Davidson Softail Fat Boy
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