Chevy II long tube headers.
63 Chevy II, Chassisworks clip, LS1, T56 tranny. I did not use the supplied motor mount adapter plates. The quality seemed good. I did spend a little time to deburr the holes and used a file to break the sharp edges. On my car the fit was good with the exception of the driver side O2 sensor. It would not work in the spot designated for it as it interfered with my stock floor pan. I ended up putting a plug in the bung and welding a new bung just downstream of the header. Satisfied overall.
5.3 2013 Silverado
I play proball and my buddy on my team has the doug thorley longtubes on his 09 6.2 silverado and he talked about it helping more with Power than even his Tuner. He wasn't lying. As far as installation goes. Just take your time and do it right. Take a day and do it right and it's not bad at all. Once you get the stock headers off putting the new ones on is not bad. Use PB blaster to loosen old headers. Much easier after