Well I'd say you feel if this is necessary when stepping on the brake pedal after changing and bleeding the mbc. I swapped my mbc a few months ago, but the truck sat for a while without an mbc at all and this probably drained more fluid out of the lines over the time. Therefore I had to crack all the wheel cylinders. Most of the air seemed to have been in the rear lines.
I constructed a simple helper for the bleeding job: fix a pully with a rope under the left front wheel, and run another rope through the pully to the brake arm. The pully gives you enough leverage to move the brake arm adequatly to bleed the brakes, and it works from all positions under the truck. Great to take along in a "care package" too, in case one has to work on a brake cylinder while being on a trip.
Bleeding the whole system took about 20 minutes with this setup, and I did it completely alone.
Cheers,
Mark