Here's a pic of several small brass/copper kettles.
The upper left one is a Jim Kimpell conversion of that common Crazy Crow 1/2 gallon brass kettle. He cuts about 1 1/2 inches off of the top, re-rolls the rim, and adds those dog-ear bale lugs and a new bale. This makes the height to diameter ration closer to the originals.
Crazy Crow now also offers a Copper kettle with proper dog-ear bale lugs. Unfortunately, it's still too tall when compared to its diameter. It holds 1/2 gallon just like their small brass kettle.
And here's a pic of one 1/2 gallon brass kettle that I cut down and then added an iron rim. This pushes the time period into the early 1700's and well back into the 1600's.
This and the Jim Kimpell conversion brass kettle all hold around 4 cups comfortably, about 5 cups brim full.
The big problem with the "corn boilers" is the way they are put together. That bottom rim is the big problem area. They tend to have a machine rolled/crimped seam, and look a lot like a modern food can. Or they have that bottom flanged/lipped out and then sealed. Those types of seams are made using those hand-cranked tinsmithing machines. And those machines only really started to be used in the 1840's and later. The most common bottom seam was the bottom disk being lipped straight up a bit all around, and the sides then set down into that lip. Then soldered together. The other early method had the bottom of the sides cut to form little tabs. Every other tab was bent in, then the bottom set in, then the other tabs bent in to hold that bottom in place. And the whole seam then soldered into place.
Westminster Forge does some good ones with the correct bottom seams. So does Goose Bay. Check them out. Jim Kimpell finally does have a web site started.
http://highhorsetrading.com/ He only had a few things on it the last time I checked. And several other tinsmiths out there also do good correct work. And more are also doing Hot-Dipped tin work.
If you find a small pot with a bottom seam that is flush, or does not look like a moder food can, then it should work. (For a quick understanding of that machine rolled/crimped seam, just look at most any "tin cup" you find available at events.)
In the end, it is all a matter of personal choice. Use what you feel will work for you. Personal choice.
Just my humble thoughts to share, and best used in conjunction with your own research.
Mikey - that grumpy ol' German blacksmith out in the Hinterlands