What are the rules differences in Empires in Arms?
I don't own the Australian Design Group version of the game, and I have yet to find a copy of the rules online in any form.
The Avalon Hill version of the rules can be found in several locations. BGG, eia.xnetz (or with Errata integrated)
This person claims that the following were changed.

Inf went from $2 to $3, ships from $7 to $10, guard and artillary from $6 to $7...
In the ADG version, all corps were uniform, ie, all French corps were 20i3c: In the AH version The french 1st corps is 25i3c, 2-6 are 20i3c, 7-9 are 15i2c and 10-12 are 12i1c. The 4 cav corps in ADG were 7cav each, in AH they are 7 cav for 2, 5 cav for the other 2. Similar corps composition changes were made to most of the countries.
Guard was added to Spain and GB, though not guard commitment.
New political combinations was greatly expanded.

Without access to the ADG rules, I cannot confirm or deny these changes exist though.