Something we need to research better for accuracy I think.
This is all the info I have from memory,see what you think,we can make adjustments as we gather more concise info:)
Mk 1 and 2 fan,Std Villiers throttle control.
Model 1 and very early model 2,chrome over copper plated cast alloy.
Model 2 full plastic (Black)
Note I am unsure whether the use of a bi material(as per your diagram) throttle control was Victa issue or a repair option for plastic assy due to base failure? Although I have seen many of your type around.
There is evidence of a green(same green as the groove cover) throttle control used on early model 2 rotos but ive yet to come across a real sample.
So black plastic for rotomo 2 and into model 2a. Then the full chrome alloy with the red Victa embossed on the cover which im certain saw out the model 2a.
Model 4 and 5 control same as 2a with the exclusion of the red embossed victa logo.
Fan,Model 1,model 2 are confirmed accurate,just need to see when(IF) your example was Victa issued and also the correct fittment for the red embossed full metal version.
Please feel free to correct any discrepencies,as ive not fully researched throttle controls,only going of what type ive seen on the majority of corresponding models.
Also my appologies for lack of images lately,my printer /scanner is cactus my comp is on its last legs and i cant find the cable for my phone sighs*.
