Replace Item Model with Item SKU on Invoices?

Using v1.4.9.3. What I want to do is, on the invoices (the ones that print at least, less worried about what I see in the admin area), replace the Model # with the product's SKU. Might be as simple as a variable change and a change to the text it calls on for the column name when generating the invoice....can anyone help me out with this?

Check this link as reference, may be help you
http://forum.opencart.com/viewtopic.php ... %3F#p90878

That does look like it would help, yep. Dunno why that didn't come up when I was searching, I was going pretty generic and usually anything with ANY of your search terms shows up.

EDIT: That post is pretty badly out of date. None of the lines match anymore, so I can't be sure I'm putting anything in the right place. The other problem is that that seems to be geared to adding the SKU column, in addition to the Model column. I want to actually have the SKU replace the model entirely in both the cart display and the invoice.

Just wanted to say, even if someone wanted to copy-paste the instructions from the post linked above, and tweak them slightly so the line numbers were correct, and they said "replace line X with this" or whatever in order to make it a change instead of an addition, that would be great.