They do TTI, though there price tag and installation process sucks they do fit well.
I just ordered a chevy long tube build your own header and sbM flange and made my own. My passenger side is very similar to Doug's. I used a mini starter, no slip fits on mine and tucked mine up much closer to frame rail. Super easy to slide in from the top.
Drivers side has cut flange with the center two headpipes going along the block together and the number 1 headpipe follows same as Doug's but has a slip fit after it turns down over the steering shaft.
If manufacturers would do a cut flange on drivers side I could see installs being easier, more routing options, and
I've never built a set of headers before these and it really wasn't very difficult. Sorry not quite in topic
