Well the Aurora kit is not really in scale or proportion so comparing the Moebius kit to the Aurora kit is moot. The big model and small model may be based on different filming minaiatures, too, which varied in proportions and details.
The Aurora Seaview is 1:300 scale according to the 1975 instructions and Moebius' version is 1:350 scale. I have both models and there are some significant differences where size and proportions are concerned. It is my understanding that the Aurora version is patterned off the model that often appeared in Admiral Nelson's quarters and not the 17 footer.
The Aurora kit is a different scale than the Moebius kit, and it is either not based off the same miniature, or any miniature at all. Comparing the Moebius kit to the Aurora kit is moot.
When you compare the deck of the small and large Moebius kits, what is it you are looking at and for? I would measure it as shown below so you are measuring the same thing on both large and small models
The BLACK outline represents a cross section of the deck area. There is the lip on the left and right hull and the deck in the middle. The lip thickness (BLUE) is not constant between the two kits, but the width across the whole area should be the same.
Measure as indicated in RED across the whole deck since part of the deck is molded to each hull side. Do not measure as shown in YELLOW.
That SHOULD give you the best measurement and the two kits can be compared more precisely.
The large kit measures 28.5mm across. I do not have a small kit handy to measure.
I DO happen to have a 350th scale Seaview handy!
It measures 10.5mm plus or minus.2mm
28.2mm x128 =3648mm
3648mm divided by 350=10.42286mm......
Looks to me like the rear deck of the 1/350 model is pretty much the same scale width as the large model......