So when I checked my compression with the crappy oreilly compression gauge, i got 120,90,60,0. the tester wouldn't hold pressure, but I'm 90% sure its head gasket, but i wanna see if theres any other opinions on it first

So, I'm new on the forum, been lurking on and off for years, and not new to dsm by any stretch. I got a 95 talon w/1g head, coil on plug, manual swap, 16g, 255 walbro....anyways, got fuel, got spark, timing lines up, and a fresh battery, all I can get is a backfire but no start, compression test...