Re: Front Disc Brakes
The fade resistance, extra stopping power and greater convenience are worth any extra weight. Especially if you're making more power than stock!
Assuming your kit included new front spindles, you'll be swapping the original spindles with them, so those should be a wash.
While I haven't tried weighing a drum and disc, here too, your probably pretty similar in weights. Also, the brake calipers, compared to the weight of the slave cylinders and backing plates they'll replace should be pretty similar too!
Add the convenience and ease of changing brake pads, the fewer moving parts (springs, hold-downs, adjusters, etc...) and no need to adjust and you still come out good!
You can always go with an aluminum water pump, aluminum intake maniufold and even relocate the battery to the trunk if you're concerned about any extra weight in front. I would be surprised if there is more than a 10 or 15 Lb increase at most. Heck, I'd rather diet a few weeks and lose that much weight!
I changed-out the rear drums in my '79 Formula with discs and love them! Plus they look a heck of a lot better and stop my 'bird with much better brake pedal feel.