the PERLLIB environment variable captured at the customer site has over 430 directory entries.

I can't be the only one who read that (twice to make sure I hadn't mis-read) and immediately thought how impressively horrendous it is. You have my sympathy.

what would be the best method to verify that the captured Perl environment at the customer site unpacks and runs smoothly on my employer's network?

Obvious answer: run the test suite. Now I'm going to assume that an organisation that has ended up with 430 entries in $PERLLIB probably doesn't have a test suite. So your first task is to write one. I would start by writing a test which just compiles everything in turn. That way you can run the test, keep adding to @INC or whatever needs to be done to get things to compile without breaking the ones you've already fixed. This will be a lot of work but it's sure to pay off in the end.

Actually, I posted this Q on Stack Overflow and the first response was to post here.

That's fine but if you could link to that SOQ then it will save possible duplication of effort in replying. Thanks.