To find all three-digit Lusophon numbers $\overline{ABC}$, we first need to establish the conditions under which a number meets the Lusophon criteria. A number is defined as Lusophon if the sum of the number and its digit reversal is a perfect square. Therefore, we need to consider the number $\overline{ABC}$ and its reverse $\overline{CBA}$, and determine when their sum is a perfect square.

Expressing the numbers in terms of their digits:
$$\overline{ABC} = 100A + 10B + C$$
$$\overline{CBA} = 100C + 10B + A$$
The sum we need to check is:
$$\overline{ABC} + \overline{CBA} = (100A + 10B + C) + (100C + 10B + A)$$
$$= 101A + 20B + 101C$$
Thus, we need to find when:
$$101A + 20B + 101C = k^2$$
for some integer $k$.

### Procedure:
1. Range: The value of a three-digit number $\overline{ABC}$ is from $100$ to $999$, so $\overline{ABC}+\overline{CBA}$ is between $198$ and $1998$.
2. Perfect Squares: Calculate all $k^2$ in the range from $198$ to $1998$.

#### Iteration over valid digits:
- I will iterate over possible values of $A$, $B$, and $C$, and calculate $101A + 20B + 101C$ for each combination.
- Check if the resultant sum is a perfect square.

Since extensive listing and checking combinations can be cumbersome manually, below is a concise approach capturing valid identities:

- Valid Calculation:
1. Pair values for $A$ and $C$ such that the expression gives perfect squares upon reasonable selections of $B$.
2. Leverage modular arithmetic and divisibility properties to constrain possibilities.

Finally, the calculated Lusophon numbers, fulfilling the criteria throughout valid selections, are:

$$\boxed{110,143,242,341,440,164,263,362,461,560,198,297,396,495,594,693,792,891,990}$$
These include all the numbers whose original and reverse sums form perfect squares, using the iteration through the digit space and ensuring accurate capture of conditions.