Some of the heel-toe technique was for older cars. Cars without synchros (like Formula Ford) pretty much require a double clutch to get synched. It's a pain and one reason why I don't run cars like that.
You don't actually brake with your heel today, although I have done it in older cars where you need to reach across long distances.
The idea is to put the left edge of your right foot on the brake and roll your foot over to throttle. You end up with the show usually hitting the throttle right around where the laces go into your shoe. You should be blipping while you are shifting into gear. Unless the sychro won't keep up (and you can outrun the Viper synchros) you want to shift as fast as you can while being smooth. There is no reason to **** the shifter. About half the NASCAR drivers don't even use the clutch: their blips are so precise that they can blip to the exact RPM needed.
There is a pretty good diagram on:
http://www.turnfast.com/tech_driving/driving_heeltoe.lasso
BTW, trail braking is a different issue entirely. Any time you downshift you really ought to be using heel toe. You use trail braking when you need to brake in a corner where high entry speed benefits you where the exit is _decreasing_ radius. The idea is that you brake while going slow into the corner, get to the apex right on the edge, and then accelerate coming out. It can account for a few feet of difference on the track, but it is only useful for some of the corners - not all of them. For the other turns, brake in a straight line.
Trail braking can screw up a lot of otherwise good driving. Braking is the hardest performance concept to learn: we don't do it at 10/10 on the street and it takes a lot to learn how to do it. I have spent plenty of time in the gravel thanks to my mistakes.
The better approach for most people is to brake in the a straight line and then turn in. It teaches you faster since you learn the brakes limits and then the tires limits separately. Once you master those, it will be easier to combine them together. The Viper has big tires, medium weight, and relatively poor brakes. That means you stand on them for a long time and then have to release faster as the big tires kick in. It's certainly harder to learn to threshold brake than most cars out there.
If you are on the track, you initial time will be better spent learning the line and the limits of the tires (both in braking and in the turns.) Once you get so that you are running with the leaders, you can start to add-in trail-braking.
If you really want to have fun, start left foot braking. I can't bring myself to do it too often, but I know that left foot braking can provide even a little more speed in certain situations.
Have fun!
-Dan