Thanks to Chuck Kutz and Tony Went

Nazareth was headlining with support acts Slade and The Ian Gillan Band (not yet known as simply 'Gillan'.) 
The day of the concert our local radio station announced that Thin Lizzy had been added. 
They played after The Ian Gillan Band and before Slade. 
I was knocked out by the band, it was the first time I'd seen them perform. 
It was also the first time I'd ever seen flash pots at a concert (on the opening chord of "Jailbreak", of course)

Chuck Kutz