The steel vs. aluminum argument is about 75 years old: "aluminum is stronger than steel, pound for pound", but that's tensile strength, and not for the same material volume. An aluminum piece can have the same strength with some weight saving, but it must be larger.
Resistance to an explosion is strength (although shape deformation during the 1st few microseconds will localize stress, and the local intensity will be higher in steel).
There's an advantage to aluminum in that the (required) larger material thickness permits threads where steel would be too thin.
For stiffness, steel is the only choice - for the same length or thickness or diameter (your choice) the Young's modulus of steel (any) is about 3 times as high as aluminum: 30 vs. 10 (× 10^6). The steel piece can be 1/3 the size with the same thickness or length, and considerably smaller (ooppss- corrected) diameter.
Vizard cautions against aluminum in favor of steel for intake parts due to heat transfer - but that's for an underhood environment where the ambient may exceed 180° F. Much less a concern with LSR. Possible exception where the plenum's charge temp is much higher than ambient, since it will cool slightly by radiation and convection and should be flat black. Any intake plumbing that goes near the exhaust or exhaust wash should be steel, plated, coated or painted a light color, and wrapped!
