Gunnera and Fatsia will be fine planted now. Fatsias are quite happin heavy ground - they wouldn't have survived in any of mine if they weren't! As long as you prep the ground well, adding some compost etc to give them a chance to settle in, and as long as they're in at least a 6 or 7 inch sized pot, they should be no problem. Gunneras do need a bit of protection over winter, depending on the type of weather conditions you have in your area. The crown can be damaged by frost, so you would need to be aware of that - especially with a newly planted specimen. If you're unsure, it might be better to leave it till spring.
The addition of leaf mould or well rotted manure is beneficial for both of them if you have it.
Eucalyptus (is it the common gunni one?) are pretty tough too. Nice well drained soil for them, so again, just prep the ground well before planting.