In the scale section I've done a bunch of "rocket study summaries" using .pdf's I've collected over the years from various sources including NTRS-- NASA Technical Reports Server. This includes a bunch of stuff on uprated Saturn V's, NOVA, and Saturn C-8, as well as Saturn II proposals, and uprated Saturn IB and solid propellant first stage Saturn IB's.
You have to realize, that these were PROPOSALS, and so not a terrible lot of the nuts and bolts technical work had been done. Mostly just "is it even feasible" kind of work, and roughly what kind of performance it could reasonably be expected to have. A lot of the proposal stuff would likely have changed before the final version of the vehicle was produced. For instance on Saturn V, the original proposal was for four engines on the first stage, and no fairings or fins. The fairings and fins came about to shield the engine bells from atmospheric buffeting from the slipstream which made the engines difficult to gimbal at certain angles, since they would be hitting a "wall" of air rushing past the stage. The decision was made fairly early on to add a fifth engine in the center, and so the outer thrust ring of the thrust structure was made wider to accommodate it. The fins were added to ensure stability of the vehicle stack after an engine shut-down prior to the capsule escape rocket tower firing to pull the capsule off a doomed booster. Once the engines were shut down there was no more thrust vector control, so aerodynamic control via the fins was the fallback until the capsule was safely away. A lot of this stuff was discovered in subsequent studies done in the wind tunnel and more intricate design work and analysis of the design. Base heating was also a serious issue with Saturn V, from plume recirculation under the base. This was a major problem with the Soviet N-1 rocket as well due to its large aft diameter and ring of 30 NK-33 engines. They lost the first N-1 because of it, and had to essentially fireproof EVERYTHING in the thrust structure because of it. The added weight caused them to add another six engines to the design in the center ring to reduce the huge vacuum effect and subsequent base heating from plume recirculation.
The reason I mention this about N-1 is, I'm very confident that the NASA engineers would have discovered a similar phenomenon would plague the C-8 design... I've never considered the original "circle of 8" F-1's to be a realistic engine arrangement for those very reasons-- it was already going to be a HUGE stage with a HUGE vacuum behind it as it accelerated through the lower atmosphere; the smaller diameter Saturn V had serious issues with it so it was a sure thing C-8 would have even more so, just as N-1 did. A far more "realistic" engine arrangement for C-8 IMHO would have been to copy the Saturn I/IB engine arrangement-- 4 F-1's in the center, with 4 more arranged in an outer ring , with space between them to help alleviate plume recirculation by drafting part of the slipstream airflow into the base region, as was done on Saturn IB (which had a series of small "scoops" on the bottom edge of the thrust structure to redirect part of the slipstream airflow into the base region to help minimize plume recirculation.) In this arrangement, it would be simple to use 4 of the Saturn V type fairings (if needed) to provide a "windbreak" around the outer engines to prevent slipstream airflow from hampering their gimbaling, as well as placing the fins, which would probably have been necessary for the same reason as they were on Saturn V-- to provide some stability after engine shutdown just before the escape rocket fired in an emergency.
As for the upper stage, there's some interesting proposals there as well... I don't recall reading about the twin M-1 upper stage, perhaps I have and don't recall, it's been awhile since I did those study summaries. The M-1 was to be a hydrogen super-duper version of F-1, burning liquid hydrogen. On some of the uprated Saturn V's I've read about proposals for using a single M-1, since it would have more thrust than the cluster of five J-2's... Basically one M-1 would have been about the equivalent of six J-2's. I've read about six J-2 uprated Saturns (which of course came about after the M-1 engine development was cancelled) and even an 8 J-2 engine S-II stage, which of course would have been lengthened for more propellant. Some of these proposals are more "believable" than others. What I mean by that is, when you consider the rocket equation and the "design requirements" for orbital rockets...
More to come... OL J R