It's very hard to document specific equipment details from Smile as all we have is limited photographic evidence and some few interviews (most of which don't deal with this topic at all). It's still worth making an effort.
By the way, Brian had bought two amplifiers in 1967 for 20 quid each but on the surviving photos he's only using one (maybe they didn't play Blag live?). Back then he had no spare guitar.