Hi Robert:

You are in Portland and your client is in Guam? Unless you are going to visit them, I wouldn't even consider this.

Even if the client decides that their stack of cheques is somehow worth more than the cost for you to format their cheques, the process will be prone to problems.

To be 100% certain that it will work, you should be sitting at their computer, testing with their specific printer and configuring their Windows. Otherwise you could do a great job in your office, but find that it won't work in their office.