Due to certain circumstances, this year things are going to be different than we had planned. Namely, we are going to heavily concentrate on protein and skip many of the veggies. 

I need to plant a protein source for critter feed (namely for chickens and some for pigs). I can get all the organic corn I want at elevator price, but I need the protein source. 

I'm thinking one option is field peas. Good protein, low anti-nutrients so it doesn't need to be cooked before feeding like soybeans. Good nitrogen fixation. The only catch seems to be harvest. I need to minimize harvest/drying/storage. I suppose I could go soybeans, but then I have to cook them, seed is much more expensive, etc.

My other option I was looking at was sunflower seeds. It seems at face value that the protein is higher, and potential yield is higher. Just more betters all around perhaps? Harvesting would be cutting heads, and likely some kind of threshing machine contraption I will design and build.

I've never grown/harvested field peas. I've grown beans/peas before, but always for fresh green eating, so I just mowed down the stalks and plowed in after season. I've never had anything to do with sunflowers (oil seed anyway, my wife grows the little flower bed variety sometimes).

Any experience would be greatly appreciated.

You can check with your extension office for that type of information assistance.
What ever happened to soybean meal as a protein source?
A friend of mine saves inputs by letting the chickens run everywhere and putting them in at night.
Dogs kill the vermin on sight but leave birds alone in his case.
His kids haven't come in the house with more than a few ticks in the last few years because the chickens eat all the bugs.
They can also eat worms when they come up when it is wet.

soybean has to be heat processed before feeding, more handling than I prefer.

My layer chickens do free range, but the meat birds are far too retarded to let run free. They don't smart up until about 3 weeks before butchering.

Ever looked into a fodder system?

Yes, and I'm planning on building one, but I can't guarantee it will happen at this point. I can still sprout and grow whatever I plant, be it peas/sunflowers/barley/etc. 

I feed my chickens sunflower seeds which I grow.  I just harvest the whole head, put them in a slatted/wired drying rack to dry. Then just throw a head or 2 out to the chickens and they take care of the rest.  

I have no trouble keeping the heads for a year from one harvest to another and actually sometimes start a new years crop off using seeds from the previous years left over heads.   Although I've also started the plants using seeds taken from the 40lb bags of black oil sunflower seeds you get at the feed store.

I grow my plants away from where the chickens roam although I do get a lot of volunteer plants just from the feeding.  The volunteer plants almost never get harvested cause the plants grown from the cheap sunflower seeds never seem to get very tall, 2 or 3 feet, and the chickens will jump and destroy the heads.

I've not done this for any other animals then chickens.

.

Fodder system with Winter Wheat. I can grow enough feed for 6 chickens on a single shelving unit per week.

Add vetch or summer millet.

Its on my to do list, but more important items are up first. 

It would really save me money if I can get it going in the next few weeks, I have 80 meat birds that are HUNGRY

I think sunflowers should be in any garden or homesteaders agenda.

For a home garden I grow a lot, all black oil seed variety.

You could press them for oil (my main reason for growing them), then use the remains as the protein source as you describe.

Here in Florida I can grow them 10 out of 12 months, they mature in <90 days, attract lady bugs and other beneficial insects, and just look good in the yard.

They don't require inoculation from rizobia, though they lack the nitrogen fixing quality that peas provide as a result. If you need nitrogen, you might look at doing both.