Overall, I found that margarine makes better crumbs - and there will be A LOT of crumb topping (just cut amounts back if it's too much).
For the image, I couldn't find my jellyroll pan so I used a 13x9 cake pan. I increased the first cooking time from 15 to 17 minutes to 25 to 27 minutes, which worked fine.
I don't know why my aunt changed the oven temperature as the cake mixes she used calls for 375. I just follow her directions.