Christine, I found a Chester R. Pelczynski listed in the Natl Archives WWII enlistment database. To see that info yourself, go to this web page, click the "Search" button for "Electronic Army Serial Number Merged File, ca. 1938 - 1946 (Enlistment Records)" and do a search with his name.
If this is your grandfather, you will see that his serial number is listed as 36215425. (Experts tell we hobbyists there are errors in this database - typo and otherwise - and to take info found in it with a reasonable amount of skepticism until confirmed otherwise.)
For suggestions on how to proceed with the info you have so far,read message #10907 in this forum. Also, take a look at the site members.aol.com/dadswar