I have the shorter pr. Making a long pr. I got the metal 30 or 34 inches long. How far back from the end of metal to where I need to drill put bolt? The end I cut to make the groves in for springs.

Let the sprung springs on the trap dictate where to put the hinge bolt holes. You need to be able to reach the springs when they are spun all the way over against the jaws. This is important for when you have a frozen otter or beaver in an awkward position.
If you put the hinge bolt too far away from the hook ends, you will lose leverage.

I did what 52Carl suggested and mine worked out great. Mine ended up about 11".

This is a pair I made last year did a great job on my 330s. Good luck let me know if I can help with anything.

How did you make the notches in the end of the setters. On mine I made a v-cut but that looks like it would work better.

To make your notch just drill a hole then grind or file It out.
Or you could just add some material to the setters you already have to make them longer.

Beav is correct I measured the steel of the trap and used a drill bit just a little bigger then cut to the hole.