Before pursuing a change, have you used the new invoice form as it comes with SI? The default templates show what you ask for with the exception of the description being on the line below the “Quantity”, etc. You just have to select the “Show Details” button.
This form avoids overflow when you have multiple tax ids, or a long description.
If the issue is that you want to access the screen with detail boxes display by default, I think that is more easily accomplished than rewriting the screens. Although the text box for the description would still follow on the line after the item details.
First try and work with what you get by default. If this causes you headaches, let me know and I’ll see what can be done.