If you make your extension and angle compensation for the lift there and are running coil springs, they will bulge out because your radius arms will be crooked. Doing it that way will not compensate the radius arms for lift.
You can do it two ways. Have the beams sent off and be bent for your lift (kinda pricey) or you can cut and extend where your talking about and then pie cut after the radius arm and compensate for the taller springs. Some say not to make two cuts in your beams, but I did. If it's properly built by a competant fabricator it will be fine. I've built 3 sets and it's worked for me every time.
Dezertrangers has the best how too for extending beams, check it out.