When you mention "redefined fields," are you referring to variant records, where different record types are stored in the same data set and an indicator field is used to distinguish record type?
If so, grab each record and use the type indicator to key into a hash of record layout definitions.
Also, I have a nice EBCDIC ascii/hex dump module here. If you'd like to give it a try I'd be happy to ship you a copy. It dumps ASCII with non-printables masked with dots followed by a two-row hex dump of the source data (unconverted), and can print a ruler line above each record. I use it to dump EBCDIC data sets to files for reference while I'm working on conversions and I've found it quite handy. I plan to submit the module to the CPAN one of these days and I'd love to have some folks test it a bit and suggest improvements.