Where would I find the value of these pieces of equepment when they were new? What were they?

Question

1976 mac dump truck , 1997 protrak pinal hitch dovetail trailer, 1998 catipiller 416C

Answer 1

The 1976 MACK dump truck was roughly 30K new in 76
The 1997 Pro Trac pintal hitch trailer was probably about 10 K or more depending on it's weight capacity and configuration.
The 1998 CAT 416 C retailed for around 60K
This sounds like a set put together for construction purposes. Probably grading, if I were to have a guess.

Answer 2

Edmunds or Kelley Blue book. I know they have prices on cars, trucks and motorcycles. I never have looked at heavy equipement but it might be worth a peek.