Haha! I'm with you on that. I sometimes buy stuff when the situation is convenient and then pack it away in a box... "Good, got the part, Now I'll get to installing it when I get a chance." And then open the box a year later and it's like a birthday present because I didn't even remember I had it! Squirrels!
On edit - Took some pics of my festoon (does that sound clownishly dirty?). If you look closely, you can see what I had to do to the bulb clips to get the larger festoon to fit. I used a carbide burr on a dremel. Don't get tiny brass slivers stuck in your fingers (or eyes):
And even though you can't tell much because there's nothing else to compare it to, here's the obligatory "ON" pic: