You are gonna have fun with those two rear plugs--a couple of small access holes in the inner fender wells might be a great time saver!
Equal lengths are nice, but not a big deal with the firing order of a V8 (unless it has a flat plane crank). In fact, a little variation in primary tube length will give a broader torque curve. However, most headers leave a lot of power on the table by not optimizing primary size and length, collector design, and secondary size and length. That's the beauty of building your own! What size tubes are you using?
