I've started swapping the OEM aircon setup out of my 76 260 into my 1/75 model.
I've noticed some interesting things in the process.
I was planning to just install the cooling unit straight into the already fitted dash unit. Thought this would be fairly simple job. Turns out the cooler is too large to fit with this setup which uses all the mechanical operated flap controls. The vacuum actuated setup allows the cooling unit to sit lower behind the front panel controls.
In the end I swapped the complete control unit from the donor car which has the later model vacuum operated controls. Then when I went to plug in the fan blower unit found it to have 6 pin plug on newer unit as opposed to 4 pin on older model. Grabbed the donor car fan unit and noticed blower on new unit is rated 160w compared to 80w on old model. Fan speed control also had changed to 4 speed instead of 3, hence the extra pins. I suspect they must have beefed it up for a bit more oomph to blow through the cooling unit.
Oldmate - looks like I found the same thing as you. Should have read up yesterday before I started. Did you find the same thing with your blower fans?