The 348 and 409 are an absolute bolt in replacement for BBC and SBC in regards to the trans, flywheel(s) block-mounted starter(s) and side engine mounts. Those engines only came in big cars, though, so there weren't any stock rear dump exhaust manifolds made. I had a 60 El camino with a 348 and t-400 and it barked the tires when it shifted. The third link bracket actually peeled the axle housing metal!
Also had a flatbottom with a 348...great ski-boat motor!