I dont know you,nor do you know me. However,I have followed your Jensen project closely since being in this greasy business over 3/4 of my life(and,no,Im not 80) I worked on quite a bit of those things when they were current, and I know how precious parts can be for those things. Having built a few engines over the years, from VW to Miata to BDA Escort to 911 toV12 Ferrari,I can only respectfully recommend that you do NOT try to clean the crank with a crocus cloth, but bite the small bullet now,strip it,and send the crank,rods,AND block to a precision machine shop. Best of luck.