I wasn't around in the 70s mate so wouldn't claim I remembered it, I do like to research some of these football claims though such as Newcastle being big(they are historically fairly big at least domestically anyway but not bigger than City) it's interesting what you can find out and how a lot of clubs sugar coat things(Liverpool and United for example).
I did say it depends who they were up against, also because of the lower prestige not all the big teams would prioritise that competition, just as some don't the Europa League or the League Cup these days.
Juve, Napoli and Liverpool for example were in it that year, just looking back at it now I noticed Hamburg even pulled out of the competition themselves at the quarter finals stage, which doesn't look great unless there was a good reason for it.
Newcastle's run was:
1st Round
Feyenoord Rotterdam
2nd Round
Sporting Clube de Portugal
3rd Round
Real Zaragoza (Spain)
Quarter-finals
Vitória de Setúbal (Portugal)
Semi-finals
Rangers FC
Final
Újpest FC (Hungary)
I think that proves my point, some good teams in there fair enough but not supporting the "tougher to win" shout not that year anyway. I'd say it was about the same as the European Cup Winners Cup but perhaps without the prestige perception behind it.