You couldn't do a blowthrough with out using injection. The mixer wont deliver any gas with out a vacuum signal. The mixer is flanged onto a carb. (In this case I would use an old SU, but use it as a throttle body only) this delivers gas (and air) into the intake. Theres nowhere to blow into.

What I would do is enclose a four inch cubic water filled core, (like a heater core) inside a sealed hopper type thing. This would sit directley on top of the stock intake manifold.
Picture a typical blowthrough set up, and picture the charge feed into the manifold going into the top of the inter cooler hopper. (imagine the core is in a box with a funnel each end) the water is circulated through the core. Instead of having a seperate exchanger front mounted, (more weight etc) using an electric pump to circulate water from the converter, thriugh the core.

As mentioned previously, butane boils at 0C, and propane boils at -40C. there is no way the charge will be cooled below 0C once the turbo has compressed it. Hence, the droplets cant fall out of the charge. (unlike with petrol. that being said, some supercharged V8 race motors, espeically ones in boats) do use a water fed chiller between the blower and the intake)

Having given my original guestion a bit more thought, I now realise what I really should have asked was " How much will a turbo heat air at cruise throttle?"

A turbo might well be able to keep the converter from freezing just from the heat transfer from the charge ON BOOST. But at cruise throttle, converter freezing might occour.

I spose that I will have to build a set up, and them experiment with the intercooler part after that.

Bart.