Mite,
.36 gallon of melt I doubt seriously will suffice the capacity needed to fill all bobs, gating, and cast product. How deep is your furnace from the lip where the lid sits atop the furnace wall, inside, to the top of your crucible base? Whatever that distance is, subtract 1 inch. Also, what is the diameter of the inside of your furnace wall (in inches, please
). Whatever the diameter is subtract one inch. The maximum you'll be able to melt in that cavity will be whatever those dimensions are minus the circumference of the inside wall of the pipe you decide to use as a crucible. An ideal furnace will allow 1 inch clearance between the crucible and the inner wall of your furnace, and 1 inch clearance between the top of your crucible and the bottom of the furnace lid.
Using steel pipe for crucibles, generally, is not a good idea as the melt within them will absorb contaminants of the steel and cause a certain amount of gas issue if not fired carefully during the melt process. What is required is a very slllloooooowwww heat build up and never allowing your crucible to get beyond a minimal cherry glow. You do not want the steel to blister and scale. Too hot (bright cherry glow) will begin to cause the steel to off gas some of its properties and thus your melt will begin to absorb it. The meltdown needs to be done at a very sloooooow controlled pace. When you see the metal begin to (ever soooo slightly) develop a barely noticeable pink-ish hue, and your crucible is not much brighter than a very dull (minimal) cherry glow, THAT is when the melt is properly up to temp and will be ready for furnace shut down, purging, and then pouring. I would also highly recommend using the blue cake (tidy bowl product) I recommended Dallen use on his cast. This stuff will work very aggressively at removing trapped soluable hydrogen gas that those scrap rims, pistons, and engine case components are historically known for when remelted.
Further, to help shield your melt from being contaminated with a steel crucible's use, do a healthy pre-spray lining inside the pipe crucible with automotive primer paint. Any rattle-can product available to you in stores will work as long as it's intended as an automotive primer. A stove black spray paint, or exhaust manifold primer paint will also work. As the primer heats beyond its ability to withstand it will lose its color but still remain on the surface of the metal. Aluminum will not stick to it, and it will help keep the steel contact away from your aluminum melt.
If you cannot find any blue toilet bowl chemical cake in your stores, then I'll send you one. One cake will handle a multitude of casts, all it takes is just a pinch of it, about a thumbnail size chunk, inserted into a perforated thin walled steel tube (fixed to a length of solid rod stock as a handle) and just plunge the tube and chemical chunk into the melt and stir till the boiling ceases. The slag developed will be a host of crap the alloy has in it you don't need in your product... and it flares off the hydrogen gas bubbles as well. And yes.... you would paint the rod and perforated tube with the primer paint as well before insertion into the melt.
I'll have to mull over your thoughts and photo regarding the gating and reservoir configuration this weekend to effectively give you my opinion as to whether your intent will work or if it needs some modification.
Frank