Aluminum vs Steel chassis and tools

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I am at a case dilemma. I can get either a steel hammond case with cover in 8x10x2 or the same size case in aluminum from them.

I don't have a hole punch for my 9pin or octal tube sockets for my 6bm8 p-p amp. Heres my questions

1. can a 3/4" and a 1 1/8" hole saw be used to cut socket holes in steel?
2. If I choose Aluminum will the case bow under the mass of the power transformer and the two p-p 8k output transformers? the power transformer is a 200ma unit. Should I install wooden dowels under the chassis to act as ribs to prevent case bowing?
 
I have a Hammond organ with a 30 lb 450 V @ .5A transformer mounted on it as well as two 47 ohm chokes. It is aluminum and stands up very well.
If you have a little money, the best 7/8" holes (actually .895") are punched by "1/2"" conduit punches from greenlee, as sold by home depot etc. Last time I looked they were $35. Requires a 3/8" pilot hole in the center.
I have never had any luck with hole saws except on wood or plastic. When I have to drill a big hole in sheet metal I don't have a punch for, I draw the circle, drill a lot of little 5/32" holes inside the circle, and connect the dots with a Stanley tungsten carbide rod hacksaw blade. These are round, grey, about 3/32" diameter. Takes a 3/8" hole to get the tab of the stanley blade through. These are about $8 at the hardware store. You need a vise bolted to a bench to hold the chassis still while you are drilling.
If you have the right size drill and a drill press, clamp the sheet metal between two pieces of wood to keep it from bending when the drill goes through. 7'8" drill bits cost about $35 and tend to shatter in sheet metal when used by amateurs.
Use safety glasses when drilling. Have fun.
 
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Another option is a thing called a step drill. I got mine at Harbor Freight.
 

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