The Venkman Hero Pack currently in the Sony Archives has two rectangular unpainted sections on the motherboard at the bottom two mounting points. They appear to be identical to the upper attachment point where the half-moon spacer once was.
Where have you had a close look at that pack? Are there pictures floating around from private collections that you've seen? I've seen some of the "forbidden" photos of that pack but none where you could see what was going on with the mounts. Personally, I am pretty much in agreement with you DVC to an extent, but I think I side more with Julz. Since I posted my findings in this thread, i've gone and done my own research into this further. What I speculate is that there are either wooden or rubber blocks on the GB1 packs and not one solid piece (as you see on the PIH Hero). The Spengler gif and the other images that Julz posted perfectly highlights the details I found on the 4k blu-ray. However, I don't think they are a standard cut block shape. I believe one side of the blocks are cut at an angle which face outward of the mounts/cyclotron. It's a detail easily seen in the Stay Puft fire picture I posted previously. Harry Bardwell displayed this detail as well.
Now, I think its safe to assume that these blocks were either made from wood or another material like a rubber isolator. I am also going to say that I think that these spacers were all made from the same material as the half moon spacer. It just wouldn't make much sense not to. (The details of the half moon spacer have already been discussed before. For those of you that are unaware, Julz started a thread that covered the details of that spacer. That thread is located here: http://www.gbfans.com/community/viewtop ... =2&t=30726
Everyone in that thread had an opinion on what they thought the material was. Whether it be a hockey puck (decent guess but hockey pucks are way thicker than the size of the spacer) or something else. The two best guesses I would say was either wood or rubber. The rubber isolator theory is very plausible too since they are commonly used in aviation (which where a lot of the prop parts ended up coming from). However, I very much believe the parts to be wood and I will give you my reason why.
At some point between the first film and the second, we know that this detail was changed to the aluminum spacers when the retrofit took place. Why would they bother to change this detail? Probably the same reason why they changed some of the other details on the packs. It's safe to assume that these packs were improperly stored in a prop warehouse where parts either fell or broke off which needed replacing. Just look at the stuff that was changed in the retrofit: elbows, crank knob, ribbon cable, etc. All parts that could easily have broken due to age or been caught on something, pulled off and lost. Also, it's easy to tell that the hero packs became a lot more "worn" in the second film. Again, other signs of possible improper storage?
Another thing you might want to consider is natural weather conditions. These packs could have been sitting in a studio storage shed and had been exposed to bad conditions. May have caused the elbows to split and break apart? Possibly caused the original ribbon cables to wear down and fall apart? We all know that wood is a material that can easily get destroyed due to improper conditions. Now with rubber; not so much. Thick rubber can go bad but the conditions usually need to be extreme and exposed for long periods of time. Wood can get warped or expand much faster in harsh conditions. Bad conditions can ruin certain types of wood in a matter of weeks. Sitting in bad conditions for a period of four years? Totally possible. My guess is that these spacers were in fact wooden and ended up getting warped or cracked to the point of them being useless. We know that without some sort of spacer between the mobo and the frame that the bolt doesn't secure right and properly hold everything together. I'm thinking that's the exact reason why these were replaced with aluminum spacers.
The most logical reason for the retrofit being done on the hero packs was due to bad parts needing replacement. Why remake wooden spacers when aluminum ones require no tooling and will better stand up to time and the elements. Also, just to note that I have a rubber mallet that used to be my grandfathers. It's probably over fifty years old and its been exposed to harsh elements. I live in the desert where temperatures reach 130 degrees in the summer. On top of that, my garage is not air conditioned and gets even hotter than that in those months. That's where the mallet has been stored for at least the last 30+ years and it's only starting to show signs of hardening and cracking. Without actually providing concrete proof, I still remain skeptical on what the actual spacer material is. However, I think it's safe to say that the spacers were wooden.