Step 1: Largest possible bag size
Equal bag size must divide each heap \(\Rightarrow\) use \(\gcd(435,493,551)\).
\(\gcd(435,493)=\gcd(435,58)=\gcd(58,29)=29\). Also \(551=29\times 19\) \(\Rightarrow\) \(\gcd=29\ \text{kg}\).
Step 2: Number of bags
Bags \(=\dfrac{435}{29}+\dfrac{493}{29}+\dfrac{551}{29}=15+17+19=51\).
\[
\boxed{51}
\]