You're in luck because this is all fresh in my memory!
I just put the motor back in this week, and this is the best advice that I can give for installing headers:
Jack the car up and place on jackstands. The taller, the better. I'd suggest at least 16-18 inches off the ground at the point where the frame rails meet the trans Xmember. The tall height will help this job immensely because the headers will come in from UNDERneath. The starter needs to come out. `Unbolt the bolts that hold the motor mount to the K frame. You will need to find a way to lift the engine, either by use of an engine hoist or a floor jack under the oil pan (USE a block of wood to avoid denting pan) Install the RH side (Cyls 2468) FIRST. The LH side header has to go in WITH the starter at the same time. There is only ONE header that I know of that allows you to install the header first and starter afterwards: Schumaker. I have used Hooker 5903 and 5209. They are a different design than TTI, but still require the starter to go in along with the header.
The engine needs to be lifed up until the trans bellhousing contacts the tunnel to have enough room to slip the LH header past the power steering unit. Manual equipped cars would certainly be easier. I think thats pretty much it. Any questions? PM me or just repost. Good luck!