I can see why you would enlarge your Skyrocket plans; thing is though even small increases - let alone a 20cm (8") increase in size mandate significantly bigger engines.

I have come up with a mod that allow for the cowls to be built very scale. It is something that will require time and effort, naturally. Retracts, these are a given; cannot imagine any WW2 fighter aircraft or any scale aircraft without them. Pneumatic ones, for that matter, Robart-made which I've never had an issue with in over 15 years of operation.