I'm redoing my 67 Barracuda too and have faced the same choices. 340=larger bore, shorter stroke. Stroke a 340 and you end up with more displacement than stroking a 360, all things being equal. I believe 340's have a higher nickel content in the block. My 340 standard bore has no lip on the top. My 360 has a noticeable lip on it. If you are replacing almost everything, the cost is going to be about the same and they should both run nice. My choice was the 340 but I am keeping the 360 as a backup. For you, buying the 360 block would be cheaper than buying a 340. As far as the rest of your questions, yes you will need the 73+ centerlink, yes the steering column will work with a 73+ front setup, I don't know if the center link is the same for /6's and V8's. Questions you did not ask but should be answered, be sure to take the prop valve for the disc brake setup off the 73+ car. You will need it. Things like brakelines, hoses, rotors, calipers, etc. can still be purchased from NAPA or Advance auto. You can buy the whole front rebuild kit from Mancini. You get Moog parts and get everything except the Idler/pitman/and struts. I bought those from Just suspension but Mancini also sells them. Get polygraphite mounts for the strut rods. Oh yeah, you can also get swaybar endlinks from mancini but Napa has them cheaper. You currently have manual steering so plan on keeping it or changing out the column if you decide to go with power as the columns are different for manual and power. That is about it. Oh yeah, if your LCAs don't have the swaybar tabs you can buy them with the bar itself and weld them on. For some reason, They don't seem to mount in the same place as the originals do though. At least not from what I have seen.