Another, fairly simple way: since your data is so regular, and since all the elements are delimited by whitespace, you can simply parse it as a list of sets.

#!/usr/bin/perl -w
use strict;

open Spg, '<', 'spg.txt' or die "spg.txt: $!\n";
my @list = split /\s+/, do { local $/; <Spg> };
close Spg;

while (@list){
    # Output 1 and 5...
    print "@list[1,5]\n";
    # ...and throw away the first 7
    splice @list, 0, 7;
}
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