Do you have a backup of the old version? I can share you PayPal standards module if needs be?
In regards to the upgrade ...I just posted this on the dev site:
"Will this work instead of Knowbrands OPC or will it replace it? We've had an absolute nightmare getting the OPC module working correctly and to be honest im terrified to install this new module in case it breaks our store."
Happy i didnt dive right in. Fingers crossed for you- i'll watch this thread.