I clipped this narrative from Cecil's previous post, thought I'd add it back in to this conversation:
I forgot that I have the document of total 61 car production showing the 142 409 equipped cars but that makes it even more mysterious since total 409 engine production was 265 complete engines shipped out of Tonawanda. If you add the 84 shortblocks the total comes up to 349. If only 142 went into production cars then unless they were available to the marine and industrial users that makes 123 engines to sell over the parts counter and to sponsored racers. Where are they?
From my research notes:
RPO 580, 360 hp 409 suffix Q was added on 10-13-60.
The records show production of all W engines for 1961 ran from June of 1960 through 25 July, 1961
. Those production dates include all W engines. The 409 was added in October and the earliest 623 block I have heard of was cast November 7, 1960. That makes roughly 9 months of 409 production. and I'm guessing the demand went up month by month after the first 409 cars were introduced in Jan, 61 peaking in the last few months. Total 409 production including the shortblocks totals 349. If the rate were linear, that would be 38.3 per month, but it wasn't linear so early cars/engines should be few and rare while later production should be more prevalent.
265 is the total number of complete 409 engines shipped under part numbers 3795507 (115) and 3814301 (150). It included over the counter service, but there were another 84 "Half Motor, RPO 580"'s (shortblocks). I have to wonder what happened to all of them? I'm sure a lot of them were destroyed in racing and probably more than we know still waiting to be discovered.
GM references dated 6-8-61 show the Q now called RPO 580 High Performance (360 hp), and QA added as RPO 580 Special High performance 380 HP. QB suffix codes were also added. That would seem to support, along with written magazine articles from the day, that the QA 380 hp version was built late in the year as RPO 580 Special High Performance and the QB engine was built under RPO 587 although production records don't show any RPO 587's built unless they are the 10 COPO's. The 690 heads and 068 block came out in late May to June and would have been installed in very late production as RPO 580 Special High performance 380 HP. Any left over 623 castings would likely have been used on the 360 HP RPO 580 High performance orders. Total 409 production for 61 RPO 580 shows two different part numbers , with 115 engines under the first version part number (3795507) and 150 under the second part number (3814301) for a total of 265. I don't know for sure what changes were made to the engine to cause a change in part number or when it occurred in production, but it seems doubtful that the second version was the 380 hp since that shows under a different assembly part number . They might be out there mistakenly assumed to be early 62 068 blocks, but they would have June/July 61 casting and assembly dates. More research is needed.
Records show that there were 10 COPO W engines built for production in 61 with a different part number than the other W engines, although the part number isn't the same as the part number shown for the RPO 587, without the Parts List there is no way to determine what their configuration actually was, but these could possibly be the 2x4 version of the 409 before it was officially added as RPO 587......purely conjecture.
As a matter of interest, there were also 34 COPO Powerglide W engines built. Could be those 61 348's with powerglide like Dan (Tripower) has when, supposedly the 348 wasn't available with PG except with the 305hp.