That’s amazing, major props to you
Heh... "props." I see what you did there.
Was it true that the harness weighed a hundred pounds?
I honestly have no idea. I wouldn't be surprised if all four tentacles + the "girdle" weighed a hundred pounds (if not a bit more). 99% of the parts were cast in expanding rigid foam to try and keep the weight down, because everything was electroplated (and was spectacular).
Do you have any stories about your time working on that film?
Most of my memories from my time working in the industry are of the people that I worked with. When I think of that job I think of a good friend who was instrumental in getting me on that crew, and I recall that his first child was born when we were on that show. That friend died in December of 2015 at the age of 48 from cancer (most likely industry related).
But I also remember that a lot of my time on that show was spent creating the "secondary tentacle," which was the smaller, tapered, whip-like tentacle that came out of Doc Ock's upper main tentacle - he used it to grab Aunt May, MJ, and Spider-Man himself, during the fight on the train.
If I remember correctly it was about 8 feet long and the number 145 sticks in my memory - there were (at least) 145 individual "vertebrae" (all hand-made) and I think each one was only about 1% - 2% smaller than the one that preceeded it, from root to tip. Back then (2002 - 2003) 3D scanning and 3d printing were just beginning to be a thing - the tips for the secondary tentacles were mini 3D prints of the full-size tentacle tip that had been scanned.
Here I had just completed assembly of the first secondary tentacle (minus the tip, which we were still waiting on). So to celebrate, of course there was some goofing around and silly picture taking.
I think I did 2 or 3 of them altogether, and then there was an animatronic version (which was handled by a different department) and a couple rubber stunt versions.
I also recall that I met John Dykstra on that job - he was a VFX designer for the film. You ever hear the saying "don't meet your heroes" ? Yeah... that.
And costume designer James Acheson was at the shop pretty regularly - he was a very cool guy. He was costume designer for the original
Highlander - I got an autographed copy of his original concept design for the Kurgan costume.

He was also costume designer on Terry Gilliam's
Brazil (which is my absolute favorite Gilliam film). I remember one of my comrades in the model shop ribbing him about the shoe hat design - he confessed that he had nicked the idea from a French fashion designer from the early 20th century.
So that's the sort of stuff that I remember.
Good times... (mostly)