Ok, let me try to answer you questions. When the gas engine was on it, it was still a log splitter, who ever manufactured the log splitter" I dont recall the brand" made that machine to be a log splitter with what ever safety requirements are required for that piece of equipment to be sold to the public. A couple of guys got together and built this so called bend test machine, from scratch, using some of the parts from the log splitter. There was no adapter. As far as having the machine evaluated and tested, someone has to be able to prove that the machine is safe and operates properly and to certain standards, Art 90.7 talks about this. You cant just start building machinery and put it into use with out having inspected and and approved for anyone to use, if you do, your just asking for a lawsuit. Maybe I should also say that this will be used by students and in a classroom setting. Here is my whole issue, it's not safe, it was conjured up in someone's head and pieced together using parts from a machine that was designed for a completely different purpose and according to out AHJ, if I do anything to this thing I could be held liable and i'm not going to chance that.
Lots of things are fabricated in the field, some completely from scratch, some using components of an item that was made by someone else.
Listing is just a third party investigation of that item that says it meets certain criteria for them to list it, and it is still listed for a certain purpose, if you are not using it for that purpose the listing doesn't really mean anything.
How would we ever have all the millions of things we have these days if every single piece needed to be "listed"
UL does evaluate more then just products that are electrically operated - though electrical seems to get the lions share of recognition in UL listed products, and of course is a big topic of discussion in a forum for electrical professionals.
Whether or not something is required to be listed is a whole other issue. If the motor installed on this rebuilt machine is a general purpose AC motor - it likely isn't listed, or at least required to be listed. About only ones that I am aware of that are required to have listing are ones use in some hazardous locations.
When it comes to electrical design of the machine - the general rule in most cases is if it has a listing and is used per the listing requirements- it is ok as is. If it doesn't have a listing or is built by a UL approved control panel building shop, etc. then it usually has to be designed in a way that complies with NEC, which may be more restrictive on many things then a NRTL listing for a similar final product.
If there is no AHJ to reject the machine's installation or use, then nobody cares - until someone is injured by this machine - then litigation procedure ends up putting blame on someone, and if at a place of employment safety policies start to get tighter.