Yes, sorry this isn't more clear.
If you want more than one pen, and want one of your pens to have the INVERT engraving, just add $20 per pen for that engraving.
So if you want the T1 and T2 you can pledge for the 'Early Backer' $99 reward. You then can and the INVERT engraving (+20 per pen), or the standard engraving (+$10 per pen) OR the Blue-Flame finish +$10 per pen).
Another example: If you want two T2 pens, select the T2 reward. With "Early Backer" pricing they are $52 each... so two pens are $104. To add the engraving or finish that you want, add the following amounts to your pledge:
>> If you want the INVERT engraving - add $20 per pen
>> Or the standard engraving - add $10 per pen
>> Or the Blue-Flame finish - add $10 per pen