Hi Steve,
unless your Capri is an "every day car", or you're sure to run it for a few minutes AT LEAST once a week, it will end in tears.
I'm aware you're in WA and if you can use the "air" regularly, then it won't effect a powerful engine like the Essex V6, especially if you fit the modern rotary compressor like a Sanden. Unit of the day was a York reciprocating pistons type which were quite problematic: My 1978 XC Falcon Coupe is fitted with one which i don't use as the car only sees the road once a month, which is not enough for a York System. So it sits there adding weight, which I will not remove due to buying the XC brand new in 1978 and want to keep it original. Maybe one day I'll re-instate its operation if I can use it more often.
An evap small enough to fit inside with the heater element that constantly remains hot with no "off tap" may be a no-no. Try and give it its own box and fan for best results, if room allows. Maybe remove the heater altogether if youre in a particularly warm part of WA ?
Bernie