Re the "lots of movement" in the steering wheel..... check condition of ragjoint, the tiny (unobtanium unless in Europe) U-joints, and after that, my guess is that it is all in the rack gears. Rack is simple deal.....only two moving parts! Clean and inspect rack and input gear for wear/play.
Front end is pretty easy to take apart. Upper shock bolts can be fun... Upper a-arm bolts could give you pain if they are corroded in place. Clean and grease before assembly..... Nothing really major....not much to it all. If you unload both sides at once, sway bar connections will come apart more easily. Be careful not to damage threads on outer tie rod ends when taking it apart. Use two hammer method to "compress" the steering arm end, to pop the end joint out of the arm. The parts on the steering rack ends to the tie-rods are specially modified parts in some cases. Not "off the shelf"! (This may not apply to late cars)
Boss 302: ......after fighting with the crummy fitment of the headers with my Boss, the raised motor mounts, air cleaners that wouldn't fit, and more..... namely being the 331 5.0L based SBF engine that I put in place(!).... that engine ran SO much better than the Boss......BUT, the Boss had issues due to mod's meant to "de-perform" it to make it more driveable.....which didn't quite work..... It should have ran and performed better!
As for your "franken-manifold".....tough call! I would have offered you my "franken-headers" from my car, BUT, they were 2V port sized...not the 4V that you have! Is there ANY chance that a 70-73 351-4V right hand manifold might be more easily modified and substituted for your chopped up Boss manifold??? If not, I think I might be inclined to go for a new header....with the ugly being the fact that you're not going to find anything out of the box to fit! Although, that said, you could have some luck perhaps, with a set of Pantera headers to start with! I think I have a couple of sets of original exhaust headers with slightly eroded end flange areas (at muffler end) but the top section may serve as something to start with???? May be easier than a flange and a "box-o-curves" kit that you would likely need!
Here are some Pantera headers that I have, some have cracks in all the normal places.....! So good candidates for mod or copy.
Gotta go play plumber...ugh.....!