If you had modded the hell out of the ETA's then they might be quicker than the M42. I have had some stoplight races with ETA's in the past and they got smoked. The M42 cars are by no means fast, but the ETA's are still slower.
That said, go check the car out. If the motor makes any diesel / grinding noises then you are in for potentially expensive engine maintenance. People let one little $40 part go, and it causes $500+ in parts to poop out, possibly $1000+ if it gets to a certain point. Namely, the timing chain tensioner piston goes, allowing the chain to slap around, wearing out all parts in the timing train, usually shattering some roller shells, which can later be sucked into the oil pump, destroying only the front half of the motor if you are lucky. Phew...
Go check it out. The M42 is not forgiving like the M20 cars, you have to revv the dogshit out of it. It is very rewarding, but takes some getting used to. Either way, an E30 is still loads of fun!