These OEM junction blocks help add accessories, NOS or other, and make adding (OEM-style) fuse holders literally a snap. Still fairly available in good, NOS condition.
How to Rebuild and Modify Chevy 348/409 Engines Car Tech SA210
27 October 2017
Good Overview
This is a nice overview of 348 and 409 engines, and their peculiarities. Includes basic information on ID of different components, general rebuilding considerations. Wish it listed casting numbers for most desirable parts, such as heads, and so on, but it covers the basics well enough.