Can I load the item number into pp_standard.php

Hello Opencart Forum,

New to Opencart, new to PHP and hoping that I'm posting in the right place and not asking a too n00bish or redundant a question. I've Googled my Q for a couple of days but have been unable to solve my puzzle:

Using Opencart 2.3, default theme.

I need to send a CURL post to a third party vendor at payment completion in order to deliver an intangible product to my customer. (The 3rd party provides content so the Opencart built in downloads will not work for this use.)
I've successfully added the routine to ../catalog/controller/extension/payment/pp_standard.php and it works perfectly with one exception, I need to pass along the customer name, email and product item number and cannot at all figure out how to get the item number. Any of the product's data attributes will do, ISBN, UPC, Model, etc...
Is this possible? Am I looking at the wrong file? Am I a complete idiot?
Any and all help is greatly appreciated.
Thanks,
ILUSNST