SBC & 3 speed standard compatability

[Father&son56project]

My son and I just picked up a 56 3200 pickup as a father and son project. Its nice and solid and the only thing missing is the engine. It had a 6cyl with a 3 speed standard transmission. We have to keep costs to an absolute minimum right now, but as we need an engine anyhow, we may as well pick up a used small block, which are easy to find. I read that the bellhousing pattern in 1956 is different between the 6 and the 8, so my question is: Is there an easy way to keep the 3 speed standard while adding a small block, or am I making a dumb newbie mistake in trying this? This is our first shot at something of this vintage, and I'd like to avoid expensive/dangerous/dumb mistakes!

Thanks!