Carb studs vs rod bolts
Not really a fair comparison. Rod bolts are Grade 8 or 185,000psi strength, and are steel bolt and steel nut, being used to compress the rod and cap. The carb studs are Grade 2, are just screwed into the aluminum and lifting just by the threads in aluminum. Even if you are using better bolts in place of the carb studs, say Grade 5 or better, you are still just lifting by the threads. With how easy it is to strip threads out just with normal use, I really don't feel safe lifting 550 pounds by them. I could go on about the tensile strength of the bolts and studs, and the shear modulus of the average aluminum casting, and get technical with engineering equations, but that would really serve no purpose.
The four 5/16" bolts, by the time you take into account the depth of the threads into that diameter, are more like 1/4" in cross section. I could go out to the garage and get the exact measurement for you, but I think you get the idea. To say that that is still 'an inch' of material for lifting strength is not accurate at all. the area is Pi x R^2. R is radius of the 1/4" or half the diameter or .125. .125 x .125 x 3.14159 = .049 square inches of cross section area. Multiply that by the four bolts and you have .196 square inches. Yes, that decimal is in the right place. Just under 1/5 square inch. Even that number is assuming that all bolts are carrying an equal load. Now, if you take just one 7/16 bolt, taking its thread root diameter of 1/2" or .500 inch, you have 1/2 diameter is .25. Put that into the formula you have .25 x .25 x 3.14159 = .196 square inches. You can see that lifting with the four 5/16 bolts has the same strength (of the bolts) as one 7/16" bolt. This is, again, just lifting in tension.
Let's just say that there are better, safer ways to lift the engine.