Here's an update to my header painting process.
I've constructed this oven 2 times already in the past. Each time I build it it gets a little more efficient and I feel a little more confident that it isnt going to blow up.
First, I start with a portable dog kennel. This one measures: H=2',W=2', L=3'
I then find whatever plywood I have laying around because I usually build this thing on a short time table and a tight budget. The kennel belongs to my step-moms mom. My brother had some 1" thick sheets of plywood that measured out to around 4' x 2'6" and 4'x4' so I ripped one at 3' and then cut the 4' side in half. This gave me 2 of the sides. Another measured out to 2'6" x 4' so I cut it down to 3'with an over hang. So I could use it as a lid to lift for heat control and incase things got out of hand. Then I cut 2 pieces 2'x 2' for the back and the door. I laid down 6 12"x12" pavers which fit the bottom of the kennel perfectly. Then i proceeded to line a side of each piece of plywood i cut with 3 layers of Costco "food service" grade industrial aluminum foil. The roll measured out to 12"x 1000' so i had plenty to work with. Cost for everything so far was $0. (My dad accidentally bought the wrong foil from Costco months ago.)
I then grabbed the partial box of 1/2" long roofing tack nails (left over from a covered patio job here at the house about 5 years ago.) And tacked the 3 layers at each corner of the sheet and in the middle,being sure to over lap the 2 lengths of foil to conserve nails.
Then I drilled a few 1/8" holes in several places on one of the sides of plywood and secured it to the kennel with bailing wire and some wood screws that I could wrap the wire around to bring it tight to the kennel.
Then I bent some small u-bolt plates that have been in the garage for about 10 years into small corner brackets and secured the backside to the kennel. Then screwed the other side to the backside and at this point I was over 50% done with my home made outdoor oven.
I used red patio brick that my dad bought from a friend of mind about 5 years ago for a nickel apiece to set the plywood sides on, to compensate for the height of the pavers i placed under the kennel.
For a heat source I picked up a dual ring propane burner from the local 97 cent super discount store. Cost was $25 about 5 years ago.
The long tube header for the inline 6 has 2 seperate components. One is a lot longer than the other. So measuring each piece at its absolute longest length. (Diagonally from flange to end of collector.) I was barely able to squeeze the longer of the 2 into the oven. I managed to get the door closed.
I'm currently going through each of the heating and cooling cycles as I'm writing this. So I will post finished product in the next couple of days.