Check out the new Bottlehead Paramount kits (4/8/16 ohm taps) available in both 2A3/300B format.
Less expensive would be the Paramour (2A3) kits with the "iron upgrade". The upgrade iron may be be available (again) in a month, or two.
Imagine many manufacturers/models offer 8-16 ohm versatility.
As far as running 16 ohm drivers off 8 ohm taps I've found the sound to be cleaner (lighter/tighter LF's which highlight the HF's) when compared to the 16 ohm taps on one of my tube amps.
Can't say either way is right as my choice depends upon the specific driver/cabinet being used.
I've gone through more than a dozen different vintage single and coaxial drivers in the past three years.
Cabinet/baffle material & construction will probably alter the sound @ least as much as impedance matching (between 8 & 16 ohms).
Want fuller/looser bass then use less rigid baffle material (just an example).