How do I change a big data file with no record separator?

[James E. Ward]

I have a task before me.  I need to change a field in an ASCII database
file.  AWK would be perfect for this, except for one hitch: the records
are 320 characters and there is no record separator, i.e. wc shows 0
lines (like, there are no carriage returns, you know?).  It seems there
must be a Unix utility that will handle this for me.  Will sed do it?
A combination of sed and awk?  All I need to do is examine the second
field in each 320 byte record and write it back out with the second field
changed.  Any suggestions?  By the way, I am doing this using MKS toolkit
under DOS 3.3 if that makes any difference.  Please email your responses to:

------------------------James Everett Ward----------------f0057 at uafhp.uark.edu
Bringing computers into the home won't change either one, but may
revitalize the corner saloon.