Hi Scanning_newb,
when I saw your object I thought that it is probably easier to go to a local foundry for casting directly and make a casting mould from it.
Nevertheless you want to know how you can do it with PhotoScan. At first I should mention that I have never reverse engineered something by myself so just an idea how to do it after PhotoScanning.
Generally I would choose a turntable solution or something similar. To scan the outside should be no problem, I think two rounds of 24 photos (one photo every 15 ° one round horizontal and one from a little bit above) should do it. The 1/2" NPT thread isn't completly scanable only a little bit of it and where it is. But before scanning remove the three little screws. and put a ruler next to your object or measure something for example the diameter for later scaling.
For the inner part I would turn the object so that it stands on the hexagon head and take one or two other rounds ideally in such a way that there is also something from the outside in your photos. Because it is otherwise tricky to combine inside and outside. Additionally you could lay your object on the side, like in your second photo, and take another round. For both use a high aparture like F22 because of DOF issues.
Then aligning, editing the sparse point cloud, optimise, scaling (if you have the Pro version) and dense point cloud generation, I won't do meshing as it is difficult to use the triangulated mesh in CAD but for later measuring it could be useful. After that you can export your point cloud and scale it if you have only the standard edition (you can do it in a 3rd party program package like Meshlab, ...).
Because your object consists of a body of rotation - the bell - and a hexagon head, I would additionally cut the point cloud in a thin slice along the rotation axis. This point cloud slice I would use in a CAD envirement to draw a curve over it and then rotate it around the rotation axis. The hexagon head could be easily measured with a vernier caliper.
To elaborate? Go to a local foundry for casting directly
Karsten