Casting saves a lot of time and material. Once you get the rough shape/casting, just a shade oversize, it doesn't take long to turn and bore it, plus you don't waste as much material that way. If worse came to worst, I could buy a piece of 6" aluminum round, about 2" thick, then turn and bore it, but that would waste a lot of material and time, just to turn down a 2" dia. x 1-1/2" long hub on one side. The aluminum round, cut, would run about $31.00 plus S&H, but there is all the excess machining I'd have to do.
The connecting rod will mostly be to shape, as cast, and it just needs to be drilled for the two shoulder bolt bushings, with a few set screws added to hold two bronze bushings. I could buy 1/2 x 1-1/2" flat cheap, and not cut any profile in it, but I'd like to get the shape I want, without all the extra machining with using a bandsaw or mill to get it. I don't have a CNC, so I do my machining the old way.
Green sand or lost foam casting would work for either, and I would make the two wooden molds to send to them. I plan on offering these as a kit, for others who want to build the project, so castings it is.
I know a few who does casting, but want to offer the job to my Gunsmith friends, who may want to do it, first.