Need a tool to fix incorrect dates in Mail!

I read my email using Mac Mail via an IMAP server. I have an extensive archive of old messages in pine folders on a Unix machine. I would like to consolidate all my mail in one searchable place, namely, my MacBook Pro.

I've found that when I move old mail folders (originally from pine or even Vax mail) from the Unix machine to my Mac via the imapserver, dates get clobbered, so that many messages appear to Mac Mail to have been created on the date they were transferred. This is a big nuisance when sorting by date and so forth.

Does anyone know of a fix or workaround to restore the original dates of old messages? Could a tool be devised to do this?

Below is an example. The 1951 date is nonsensical since the message was actually from 22 Aug 1995 (the second date shown below). But the date shown in the Mail viewer window is April 7, 2006.

From: dombeck@oddjob.uchicago.edu
Subject: Re: phone call
Date: August 22, 1951 5:50:10 AM CDT
To: KAPLAN

Date: Tue, 22 Aug 1995 10:50:03 -0500
From: Thomas Dombeck
Message-Id: <199508221550.KAA23125@oddjob.uchicago.edu>
To: KAPLAN@FNALV.FNAL.GOV
Subject: Re: phone call

Daniel,
Oct. 4 is fine with me. I will probably come to IIT during the morning to say
hello to some colleagues--so lunch would be great.

I will e-mail you a few words for an abstract on the talk.

Tom