Here is a Spectrum 1 Cab ( not mine ). I had a Spectrum 1 as my first big amp when I was 16 ( 1971 ).
I made a new baffle board and added a 2nd D-130. I'm not sure how I did it but I had them vertical, they must have been almost touching. The Spectrum II & Sentura II cabs ( same 11 1/2" cab ) had them staggered.
Johnny G.