What I don't like about those is that they need "massaging" with some heads to fit right. I have those on my car now. They were fine with my stock heads, but when I put my TFS heads on, that #6 primary where it goes under 7, I had to flatten it a little because it hit the bottom part of the head by where the head bolts go it, and wouldn't let the flange seal up flat to the head. I like those FPA's but I'm not made of money.
I agree with the fitment, but they are affordable. Where I had issues was the Engine was a 427 Roush and the block was larger around the cylinders and a couple of the tubes touched and needed some minor dimpling. They cleared the heads though. I can't remember everything about them because I installed them three years ago and haven't seen the car since. The hardest thing I remember was the forward bole on the #8 tube was difficult to access.
The one that always fights me is the back bolt for 7, . Bad thing is, when I put my heads on, I had that stupid thing all the way on before I realized the interference problem. Then I had to take it back off again, and re-install, not to mention the 4 or 5 times I test fit it.