Convince me an engine lifting plate works

[Heo]

"The plate ensures that the bolts all see 100% tension and no shear,"

This is not true unless the load is perfectly centered on the plate and there is not tilt in the plate.
(assumes chain is connected to center of plate)

Picky comment I know.

True to an extent.  If everything is torqued properly and the two mating surfaces are flush, then it becomes tricky to calculate what's going on.  The bolts wont feel any shear unless the friction between the plate and intake is exceeded and it shifts in place.  When fasteners are used properly, the mating bodies are considered solid unless external forces exceed that friction created by the fasteners imparting force.

Yes the friction created by the fasteners  between two surfaces is often greater than the shear strengt of the bolts
in a correct designed construction

[blykins]

"The plate ensures that the bolts all see 100% tension and no shear,"

This is not true unless the load is perfectly centered on the plate and there is not tilt in the plate.
(assumes chain is connected to center of plate)

Picky comment I know.

….And that shear force pretty much is nil. 
True to an extent.  If everything is torqued properly and the two mating surfaces are flush, then it becomes tricky to calculate what's going on.  The bolts wont feel any shear unless the friction between the plate and intake is exceeded and it shifts in place.  When fasteners are used properly, the mating bodies are considered solid unless external forces exceed that friction created by the fasteners imparting force.

Yes the friction created by the fasteners  between two surfaces is often greater than the shear strengt of the bolts
in a correct designed construction

[Thumperbird]

To beat a dead horse - why not better than thinking about C19.
I underrstand the theory but this is highly variable mechanics dependant on many things inclluding material hardness, flatness, and surface roughness.  We are talking about $29.95 cheap 1/8 inch plate stock, 4 fasteners over 4" apart, pretty sure in this particular general application there is not as muh friction as you think except right around the bolt heads/nuts and better if washers are used.

I think the real thing to watch out for is not the plate or bolts but poorly machined or "used" aluminuim intake threads, the major diameter is critical for tensile strength, have witnessed many an off-sized thread, even new, compounded by use that knocks the major diameter off, loose/wobbly bolts going in is a red flag.

[CV355]

To beat a dead horse - why not better than thinking about C19.
I underrstand the theory but this is highly variable mechanics dependant on many things inclluding material hardness, flatness, and surface roughness.  We are talking about $29.95 cheap 1/8 inch plate stock, 4 fasteners over 4" apart, pretty sure in this particular general application there is not as muh friction as you think except right around the bolt heads/nuts and better if washers are used.

I think the real thing to watch out for is not the plate or bolts but poorly machined or "used" aluminuim intake threads, the major diameter is critical for tensile strength, have witnessed many an off-sized thread, even new, compounded by use that knocks the major diameter off, loose/wobbly bolts going in is a red flag.

You start getting into DFMEA/PFMEA territory, but you are absolutely correct.  There are so many factors to consider, but the vast majority are likely to be outliers in the case of a failure.  Whenever I had to do a FMEA (Failure mode and effects analysis), the top of the analysis was always the obvious items.  Eventually you start getting into the highly improbable bizarre scenarios that basically mean "I am out of ideas on how this thing can fail, but I want the report to look complete so here goes nothing..."  What's crazier is when one of those scenarios happens. 

[1968galaxie]

As others have stated the lift plates work fine in nearly all applications.
I would only be cautious if intake manifold was heavily ported (single plane type - where there is less integrity)

I prefer the engine lift tilt bar for engine installations.
Makes for a more painless install or extraction.