There's not that much difference in the cams: maybe the lift, duration, or intake/exhaust point is slightly different, but for the most part, they're interchangeable. I personally have a 1.9 TDI cam in my 1.6D with hydraulic lifters (cheaper to buy that than a new one for a 1.6). Anyway, there is no interference issues, and the engine runs fine. It did however change the power profile a bit. I think total HP is the same, but the motor is more responsive at higher RPMs and a little less torquey. It's great for highway cruising, but a little less powerful/fast on takeoffs. Nothing major, just notable.

All 1.6 hydro cams carry the same PN (NA or TD), and all mechanical 1.6 cams carry the same PNs (NA or TD). I've heard of guys swapping between mechanical and hydro no problem.

So, if your motor is running like poop, it may not be the cam's fault (unless it's bent or otherwise damaged).