Welcome to the forums Andy
first off, I think you may be an inspiration to me and many others, considering your weight and age. Quite awe inspiring to say the least.
Do the 4k tt on the weekend and report back as soon as, then we can see the direction you go in. Once you on the forums, we should hopefully be able to monitor to assist you in changing the routine where needed according to you.
I think your determination will play a major role in you achieving your goal, all we need do is attempt to keep you healthy
on we go