Not necessarily, although it would probably be a good idea. The seal lip itself will accomodate a diameter difference of around .015" according to the specifications, but the metal ring it's mounted into likes round holes. I think I'd set up the oil clearances first, then remove the crankshaft and reinstall the rear main cap including the right shim pack before boring the counterbore for the seal. My boring bar centers itself in the rear main bearing bore to make the seal counterbore concentric with the crankshaft. I made a 1" thick flat steel plate fixture that bolts onto the back of the block using the bell housing bolt holes, to secure the boring bar.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
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