Welcome to the board, tons of great guys on here and a lot of useful threads for builds.
I did a 454 swap last year into my old 65'. The current one is more than likely going to get the same treatment. Heres the run down for your questions.
Power Steering: As stated above 73' and up trucks can be used for their power steering pumps and steering coloms too. If you want to upgrad to tilt steering and all that then just swap over the whole steering unit including the colom, gearbox, and pump. Otherwise you will take just the gearbox and pump but need the adaptor for the steering linkage. Only modification need other than adaptor is to enlongate a couple holes at the frame for gearbox alignment.
454 swap: This is pretty much a bold in affair. The trick though is you need the 73-up v8 monts, doesnt matter if they are sbc or bbc. Firewall and frame rail clearance is there. depending if you have a long or short water pump youll range from 1" to 3" clearance of the radiator. For headers you can run full length and just to be safe only notch the frame rail about 1/4" at the #1 primary, I suggest this only for torque shift of the motor, it will fit without but give you like only playing card gap. I used these....
http://www.summitracing.com/parts/SUM-G9011/ . Lastly depending on trans you are mounting will dictate xmember placement and drive shaft length. So minor adjustments for an awesome upgrade.
I honestly would just stick with a bone stock setup other than basic bolt-ons ie. headers, exhaust, intake and carb. Anything more you might as well have an endless wallet or start setting up suspension for street/strip use. A stock big block has more than enough power and torque to keep you smiling and gas mileage is still doable at normal daily driving. In the short time I had mine I was able to have a lil fun at the lights....nothing saw me other than a c5 corvette. GT ponys, camaros, and even a Lightning were cake walks. Any more questions feel free to ask, post up some pics of your rides!!