Have just been given a Spitfire, trying it today I'd say the output power is compatible with the specification which says DC input to the RF amplifier is 100mW
(the weblink is now
6v6.co.uk/transmitters/spitfire-am-solid-state-transmitter-eu)
The input is shared with the series modulator device, and I'd estimate the RF output is in the region of 1dBm, so you don't really need to worry about being DF'ed out by the Radio Police.
A fault means it doesn't tune much below 600kHz, so I'll replace or increase the VCO capacitor. The VCO is the R-C oscillator in the 4046 which gives a phase-locked output to the untuned RF amplifier. I'll also do the suggested mods to the tuning indicator LED before I embark on a QRO enhancement