Unfortunately you're going to literally burn through your rigging line with all that friction in the block. The steel will hold the heat, you have no bearings or sleeve. If for some ungodly reason the system does fail and something gets damaged or someone hurt, the insurance inspector will probably not cover it as you used home made equipment where there is a regulated industry standard. Just keeping it real.
There isn't a huge amount of friction within the block, less than I hoped for to be honest. Getting some heftier loads on it should help in that department.
It would take a LOT of friction to heat this block up. More than I can see ever happening in a tree rigging scenario.
Are you familiar with rigging rings or a portawrap? A Portawrap doesn't have any moving parts, isn't typically made of aluminum(side note, climbing gear being made from aluminum typically has nothing to do with heat and everything to do with weight) and will have multiple full wraps on it which would introduce a lot more friction than this block will see, which funny enough is the entire concept on how they work.
I will do thorough testing(playing
) with this before it ever leaves my property.
Regulated industry standard equipment gets used, and misused everyday. Consequently there are failures that happen regularly to the equipment, rated or not. Misuse and exceeding limits are probably more of a concern than anything else.
To be honest I do have one element that I am not 100% sold on but you didn't touch on it.