.......I knew the early s30s had vertical heater strips but never realised that the very early cars had nothing.
This refers - of course - to the earliest North American market cars, which were somewhat more de-contented than you might expect (part of tug-o'-war between spec and RRP) and didn't even have carpets. Heated, tinted hatch glass was available from the beginning of production on Japanese 'Deluxe' models, while 'Standard' models got unheated, untinted clear glass and would have to pay extra for the defrost. Other Export markets - notably Australia - had unheated glass too, as defrost was deemed unlikely to be required.
But why would a mid 1970-production HLS30U have an unheated hatch glass? Obviously it is non-standard for this car's production date, so why was it fitted? I see no performance advantage. There's no measurable weight difference. My guess is that it was simply available on the shelf (whether by design or accident) at Datsun Competition USA - like a lot of other parts on the car - and incorporated in their later, Grande Nosed, rebuild of the ex-Racer Brown Bonneville car.
The way they talk about the 'BRE' #46 car it seems these people want to have their cake AND eat it. Sorry, if it's not the original bodyshell then it's not the 'original' car. The identity of the car rides on Part Number One, the bodyshell. Yes, it may have a lot of parts from the original #46 BRE car incorporated in the build, but that doesn't make it the original car. It's a replica. Why dance around on the head of a pin? Call it what it is.