I also went with Atlantic (speedy tanks) last year to replace a 50 gal tank- I have no complaints either.. Was around $500, whatever company you go with should be able to provide whatever tubes you need, as well as any neoprene, which is extra $$.
Got the original drawings for my '77 dolphin from Grady's customer service, just to confirm my measurements. Getting the original tank out, for me, was a major hassle though. Plenty of us have done this so you should be able to find enough advice/photos etc. on this site.. I had only been a boat owner for a month and did it myself... if you have a hard time getting the old tank out.. I can share video of my 'tank removing technique'. :lol: