Sending unit and tank removal help

Hello, this winter I'm gonna replace my tank sending unit and put a swim platform on my 251 Catalina. For both these projects I'm going to have to pull out the tank. Is there anything I need to know about trying to pull this tank out? It doesn't look like an easy job.
Also, where would I go for a direct replacement fuel sending unit? Thanks for any help.Russ

Not sure about your specific boat, but builders have been known to use many different methods of securing tanks; tabs welded near the bottom and bolted to structure, tabs welded near the middle with straps or bolts to structure. Tabs on top with straps under the tank bolted to them, no tabs and straps around tank & structure, straps over the top of the tank to bolts on the structure, foam, glues, glass, friction, and luck. Investigate well all around the tank to be sure you've gotten any and all attachments removed before trying to lift the tank, then be prepared to fabricate tools to cut foam and other bonding materials loose to get it out. A direct replacement sending unit should be available from most good retailers (WestMarine, Marine Parts Source, Marine Trading Co, Low Cost Boating Store, etc). Take lots of photos to share, and look close at anything you have access to while the tank is out- if there are repairs needed, this will be a perfect time to attend to them! Best of luck on your winter projects- keep in touch here, it's a great way to pass the cold months!