I have played around with the R&D system a bit more and noticed three things:
Research rate cap
Research rate per month is capped at “double speed” compared to normal tech progression, no matter how much money you throw at your R&D team. The cap is reached at +3 already. This is not how I would expect it to work.
This screenshot shows research started in 1946 with different funding levels for all tabs after 3 months (0.25 of a year):
Body unlock dates
Bodies only unlock after a full year has passed (i.e. in January), no matter if you have reached the required Tech Date during the year. This is different than unlocking other stuff, which happens exactly in the month the TechDate is reached.
R&D screen misalignment
The “Body” line is showing elements from the “Chassis” line, “Aspiration” is showing “Fuel System” components:
Hope this helps!