Two choices if you want to keep the Psvane pair: leave the. cover off (will not affect sound quality). Take the cover to a sheet metal shop and have two holes punched (won't cost much). Don't fret obsessively - choose one or the other!
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Get plastic standoffs/spacers, to raise your top cover a bit. Any hardware store should have those, for pennies each, and the longer screws you’ll need. ie: https://www.amazon.com/s?k=round+nylon+spacer&rh=n%3A16413321&ref=nb_sb_noss If vibrations concern you; the top can be rendered about as stable as designed, by using a 1/4 or 3/8" thick by 1/2 to 3/4" wide plastic strip, front and back, with holes drilled, where they're needed.
@rodman99999 I like the standoff idea. Lets the tubes clear and provides some additional ventilation.
Or, if you're into replacing the tube sockets and feel like getting crazy, you could copy Don Sachs' modifications and put the tube sockets on the reverse of the circuit board and then mount it upside down so that the tubes are exposed on the top of the case.