Hello Matthew,
Does your glasses fog up in your Vader Helmet? Chances are they will fog up in a TK Helmet. What type of Armor did you order? What type of Helmet are you getting?
Depending on how much you trim out of the bottom of the Helmet, you may have to twist the Helmet to put it on. What are you going to put inside the Helmet? If you put wiring, Screws, Bolts that keep the Helmet together, Fans speakers, helmet liner, etc. Add that, with the measurement of your head, there is little left for room. Also, there is a chance that you can scratch the lenses on your glasses, with what is inside of the Helmet. I wear glasses. After, putting my AP Helmet on, I would not take the chance on damaging my glasses by wearing them inside my helmet. Others my disagree. I paid $350.00 for my glasses.They have Anti-scratch, polarized and anti-reflective coating on them. I also have contacts for outdoor activities.
I know that you mention you are short on cash. Investing in armor and supplies for building,is expensive, my opinion, I would think about investing in disposeable contacts.
Andy