Step 1: Find the radical axis of the two circles.
The given circles are
\[
S_1:x^2+y^2+8x+2y+10=0
\]
and
\[
S_2:x^2+y^2+7x+3y+10=0
\]
The radical axis is obtained by subtracting \(S_2\) from \(S_1\):
\[
S_1-S_2=0
\]
\[
(x^2+y^2+8x+2y+10)-(x^2+y^2+7x+3y+10)=0
\]
\[
x-y=0
\]
So, the radical axis is
\[
x-y=0
\]
or
\[
x=y
\]
Step 2: Understand the reflection about the line \(x=y\).
The image of any point \((a,b)\) with respect to the line \(x=y\) is obtained by interchanging its coordinates.
So,
\[
(a,b)\rightarrow (b,a)
\]
Step 3: Find the image of \((3,4)\).
Given point is
\[
(3,4)
\]
Reflecting it about the line \(x=y\), we interchange the coordinates:
\[
(3,4)\rightarrow (4,3)
\]
Step 4: Final conclusion.
Hence, the image of the point \((3,4)\) with respect to the radical axis is
\[
\boxed{(4,3)}
\]