My guess would also be the Axial .28 Spec 2S. They did have a .32 in the prior Spec 1S line but I dont think they had it in the Spec 2S line. The two look pretty much the same but the .28 Spec 2S was much more popular than the Spec 1S line, so Id guess its a Spec 2S.
So you're aware the block or casing of the engine usually has the company logo and engine make stamped into it. Or raise symbols. What does the othe side have on it. Or the pull cord.
It definitely looks like the gren cooling head of the axial .28 big block. You could also messure the bore of the engine.