The picture was a box-office smash-hit despite being generally lambasted by film critics. For example, Gene Siskel and Roger Ebert called it one of the worst films of 1982.
When the boys are weakening the bridge supports with a chainsaw, it's quite obvious that the chainsaw is not running - no smoke, no vibration, no sawdust.
The marching band at the end has Mellophones. These instruments were
invented around 1966 and didn't become popular for another 10 years or so. In 1954 the band would have been playing French horns.