I have found a conversion online which says 1Td = 2.829 V/(cm Torr) and 1Torr = 0.001332 bar and with this; 1Td = 0.3768 V/(cm bar)
However from literature for SF6; 362Td = 86.3 kV/(cm bar) where they do not show their conversion, The ratio is 1Td = 0.24V/(cm bar)
My conversion has a ratio of 0.3768 whilst literature has 0.24, what am I missing?
An educated guess by an outsider:
According to Wikipedia (whatever weight that holds for you), the townsend has the units of an electric field divided by a number density, which works out to $\rm V\, m^2$. However, the torr and bar are units of pressure. The ideal gas equation for number density,
$$ n=\frac NV=\frac P{kT} $$
requires a factor with units of energy ($kT$) to convert between number density and pressure.
In other words, your conversion factor with pressure units depends on the gas temperature.
One way to check this guess of mine would be to compute the assumed temperature in your confusing reference about SF$_6$, and see whether that temperature makes sense given the rest of the paper.
An educated guess by an insider.
Everything rob says is correct and everything calculated in the question is correct.
I have been making calculations with E/N values and I also have to convert from V/cm/Torr to Td. and I got a similar but slightly different value of 0.33 by making some approximations.
As mentioned by @rob the temperature will change things and people may generally assume something close to room temperature. My one comment for SF6 is that the ideal gas equation may not work so well for SF6 depending on the temperature and pressure and of course the temperature is critical to the conversion anyway. SF6 will become liquid as the pressure is increased above atmospheric pressure when the temperature is close to room temperature.
