By boxed off vs round you mean like these? I only looked at the engine a couple of times, but I'm thinking it is the more boxed off style, looked the same as the 22r spare engine that is still together.
According to the little research I did on the differences between the two, the later model had the intake simplified some so it was less restrictive and seems to have given it +hp which should be also more efficent or atleast the same.
36 out of the 4x4 91 sounds really good to me, but I'm assuming little to no eco mods right?