OK besides all the technical stuff, (I know of a few examples) is there ANY "visual" ways besides the block coding, to know which slant 6 is a 170, 198, or the 225?
198 and 225 are externally identical. The block stampings aren't even reliable, because the 198 and 225 blocks, year by year, are the same, the only difference between 198 and 225 is the crankshaft and connecting rods. So so who knows what's been rebuilt into what; you can't know for absolute 100% sure until you open the engine.
The G-block (170) is easy to tell from the RG-block (198/225). The G-block has a very short bypass hose between the top of the water pump and the bottom of the cylinder head; most of the hose is covered by the clamps and the whole thing is barely an inch and a half long. This hose on the RG-block is visibly much longer, you've got a couple inches of bare hose between the clamps.
