Assume that $a$, $b$, $c$, and $d$ are positive integers such that $a^5 = b^4$, $c^3 = d^2$, and $c - a = 19$.  Determine $d - b$.
1. Given the equations \(a^5 = b^4\) and \(c^3 = d^2\), we can express \(a\) and \(b\) in terms of a common integer \(e\), and \(c\) and \(d\) in terms of another common integer \(f\). Specifically, we can write:
   \[
   a = e^4 \quad \text{and} \quad b = e^5
   \]
   \[
   c = f^2 \quad \text{and} \quad d = f^3
   \]

2. We are also given that \(c - a = 19\). Substituting the expressions for \(c\) and \(a\), we get:
   \[
   f^2 - e^4 = 19
   \]

3. To solve for \(e\) and \(f\), we note that \(f^2 - e^4 = 19\) can be factored as:
   \[
   (f + e^2)(f - e^2) = 19
   \]
   Since 19 is a prime number, the factors must be 1 and 19. Therefore, we have:
   \[
   f - e^2 = 1 \quad \text{and} \quad f + e^2 = 19
   \]

4. Solving these two equations simultaneously, we add them to eliminate \(f\):
   \[
   (f + e^2) + (f - e^2) = 19 + 1
   \]
   \[
   2f = 20 \implies f = 10
   \]

5. Substituting \(f = 10\) back into one of the original equations to solve for \(e\):
   \[
   f - e^2 = 1 \implies 10 - e^2 = 1 \implies e^2 = 9 \implies e = 3
   \]

6. Now, we need to find \(d - b\). Using the expressions for \(d\) and \(b\):
   \[
   d = f^3 = 10^3 = 1000
   \]
   \[
   b = e^5 = 3^5 = 243
   \]

7. Therefore, the difference \(d - b\) is:
   \[
   d - b = 1000 - 243 = 757
   \]

The final answer is \(\boxed{757}\).