60kpsi tensile strength yields around 3,000-3,200lbs on a single G2 5/16" bolt, assuming it is 100% tensile and no shear. You can suspend a typical 4-door car with a single Grade 8 1/4-20 bolt or C12.9 M6 bolt. Can, doesn't mean should, but it gives a sense of scale to the strength of materials.
Where a carb plate can fail is:
1) Hardware is compromised (rusty bolts, hydrogen embrittlement, stress fractures/elongation from previous use, torqued beyond 75% yield or drastically unevenly, etc)
2) Chain is compromised (same as previous failure modes)
3) Intake is compromised (too weak to begin with such as sheet metal, stress fractures in castings, threads stripped, etc)
4) Weld failure (bad weld, damaged from previous use, etc)
Plus unique circumstances that I won't get into because it would be a long list...
A carb plate is actually much safer than bolting down chain to heads/intake because the load is distributed far better between fasteners. The plate ensures that the bolts all see 100% tension and no shear, whereas the chain method always put shear force on the fasteners which is the quickest way to cause failure. I have never witnessed a carb plate failing, but I have seen chains and fasteners snap when loaded improperly.
When I train up new engineers, I always get asked "how do you pick the right hardware sizes and number of fasteners?"
1) Determine working loads/moments
2) Determine default fastener size based on min thread engagement requirements (material thickness or thread engagement = 1.5x dia for ferrous, 2.0x dia ferrous, min)
3) If the working loads/moments exceed the tensile or shear strength of a fastener sized for min thread engagement, and material thickness cannot be increased or reinforced, add fasteners to distribute loading, perform FEA if application has potential to cause failure or injury (in some cases, add torque pads to prevent deformation)
4) If forces aren't the limiting factor, default to what is the easiest to manufacture and at the lowest cost (usually means oversize it, tiny hardware is more expensive than larger, common sizes)
99.9% of fasteners used on the planet are drastically oversized based on the loads/moments they see. Just for S&Gs, I designed up an example assembly using "appropriately sized" hardware and material thicknesses based on loading, and the fasteners were all insanely tiny. In that example, an M6 bolt would have been 100x oversized, but far easier for the machinist to cut threads and a builder to install than M2.5s everywhere. The assembly looked goofy and fragile, but was designed with a true 4x safety factor. I showed it to younger engineers to illustrate why not all fasteners or material thicknesses are designed solely for load factors.
https://www.engineeringtoolbox.com/us-bolts-tensile-proof-load-d_2066.htmlNow, with all that said... I pucker a little every time I see an engine hanging from a carb plate, even though the math says it is totally fine
Same goes for tractor tipping angles. I hit 5 degrees on my tractor and I freak out, even though I know a static 22.5 is safe, mathematically. Sorry for the long post, this is a subject I enjoy.
