Hi, DM,
Be sure to measure carefully and fit each piece before making final cuts. I measured as accurately as I could, but didn't have access to every spot. Many parts, especially the gussets and doubles, will have to be fitted and rimmed as you go.
Also note that the 415M cabinet depth is 18.5 inches. Someone recently posted that it was 18 even. It isn't. It's 18.5.
I'm building right along with you, but not a 415. I needed four floor monitors and posted for measurements. Nobody seemed to have any of these, so I drew them out from the best of my memory - pretty fuzzy after 40 years (I bought them in 1975). I cut all the wood, and I have all the hardware and fasteners. The cabinets have already been glued and screwed together. I just need to route the edges and trim the angle onto the top and bottom face parts before covering them with Tolex from Conrad. My monitors are slightly taller than the originals, but will look good enough to fool me when I'm finished. I'll post pics when I'm closer to done with them. Only real audio difference will be a small tweeter instead of a small horn.
Best of luck with your cab. Let me know if you have a question about anything specific.
Warmest...
