I did not throw out the original lifeline stanchions that were in my boat when I got it. I have a different gameplan for this feature. You might contact Bud Weisner about where he found the replacements - budweisner65@yahoo.com
Your plan for the extra tanks sounds good. Yep, I figured you meant the ones that were taken out had been mounted ahead of the cabin bulkhead.
I am flattered that you think my idea with the subfloors is good. It is quite a bit of extra work, but I think they will be a great addition. The floor cutout panels will be hinged at the front of the cutout and fold forward to within an inch of the cockpit bulkhead. If they try to bounce up and down, I will devise a holddown mechanism. Bill