Hello Jason:
You too huh? I bought a house and I started with a new workshop and then foundation problems. Almost two years later, workshop up, foundation done, new terracing in the back yard. Nice! Just to reassure you that, yes, things do get done, and things do improve. ;-)
Now for your garage door problem. It is not a problem, it is an approach. Look carefully at the door. Open it so you can see both sides. That door is not "manufactured" it is made. Judging from what little I can see the panels probably weren't weather tight from the outside. Is the outside edge bevelled too?
You don't need a router bit. You need a means of lifting one side of the workpiece while passing the other edge past a straight bit. Take a cedar shingle and see if it matches the angle of the cut on the existing stile. If not, stack shingles until you have the right dimension. Use that to create the angle on your router table. Now, you can duplicate that edge. There are angle bits available from a variety of manufacturers but from what I see, there is no need for that.
Your manufacturing sequence is thus:
1. cut the slot for your door panels in your stile material.
2. mount your angle jig (the shingles) on the router table and do the four angles (two inside, two outside?) being careful not to take off too much.
3. reposition your router and make the tenons that fit into the grooves on the rails of the door.
4. When you're assembling, make sure you seal the exterior of the door well. Lots of primer and then a good coating of weatherproof paint. It might also be wise to use a polyurethane glue with lots of clamps to seal the joint during glue up.
Now, you might not need to rebuild the components. Take a look at how much of the material is actually rotted. Is it surface rot and why did it happen? I'm using bondo as an exterior sealing agent for cracks and holes in wood. Yup, the same stuff you used on your old rust bucket back in the 60's. Apply liberally, sand profusely and coat with oil based primer and beauty is the word.
HTH