Got the Speed Daddy headers installed this weekend. Process was pretty straightforward with the instructions in this thread. W body dipstick worked without any modification, I can see where the H body one would get in the way.
Two things I wish I'd known ahead of time:
a) pulling dipstick tube will leave about a quart of ATF on your driveway.
b) front header flange is a different shape than the stock flange. It'* shaped to fit the gasket, while the stock flange only has material around the ports, leaving parts of the gasket exposed to accumulate crud. I didn't notice this and proceeded to tighten down the header flange onto all that crud and wound up having to remove it again and clean the mating surfaces.
The whole thing is very time consuming as a lot of the existing exhaust fasteners will be thoroughly rusted, which makes you take your time and exercise a lot of patience-- Otherwise you risk stripping heads, and that will pretty much put an end to your project. While removing the crossover from the stock rear manifold, the bolts broke off inside the manifold.
As suggested, I had to get creative in getting the header downpipe to mate up to the existing exhaust. I had a new hi-flow spun cat to put on also. With the right combination of clamps, pipe and adapters, I had the thing together solid. It did require a saw-zall and angle grinder w/ cut-off wheel to cut the various pieces and stock exhaust to the right length.
What I ended up with was: Header DP -> 3" OD pipe -> 3" ID cat -> 3" OD pipe -> 3" ID to 2 1/2" OD reducer -> stock exhaust. I hadn't realized the stock exhaust was 2 1/2" ID, so I was able match it right up to the reducer without any kind of coupler.
The downpipe to 3" pipe clamp provided with the kit was tricky, and took three or four attempts to get the flanges to match up correctly. I cut out a gasket and used it between the flanges for good measure.
Here'* some pics when it was all said and done. The black on the exhaust is some high-temp RTV I used at the joints. More than likely it'll all burn off and turn to smoke, but it gave me a little piece of mind. I was quite surprised that I have the entire system leak free using only clamps (I did purchase two 2 1/4" and two 3" torca clamps from www.frozenboost.com
as was suggested). I was almost certain I'd have to take it to an exhaust shop for some welding, but nope!