A relieving beauty...1.55 ct bought in 1981 from a well reputed dealer in Idar Obenstein. Receipt says "Siamese" but has a very intense red in lwuv indicating Burmese.
Got original receipt. Guess the price
You might want to delete one of these threads since they appear to be identical pics and discussion of the ruby.
As to what your Dad paid back in the day, based on the one pic which shows it to be pretty dark in tone, I'd guess not a lot, especially given that it was 1981! I bet your Dad would've been really happy to see your strong interest in his collection.