thats a photo looking up the bench towards the water heater in the alcove i was talking about, the heater itself stands 54 inches high and has a 25 inch diameter, if you include the pipes sticking out the side its about 33 inch wide sideways.
now because these things usually blow up every few years i have to make sure i can get access to replace it so thats why i have decided to climb the track up and have a turn around above it. The total width of the alcove is about 5 feet so i was thinking i would have a 24 inch radius turn around up there and leave aliitl room on the side for a tool rack i have there and a small set of steel shelves you can see in the picture,
the benchwork im building for the layout stands 44 nches high and is 33 inches wide on a 21 foot run down the wall. i built the bench so far to my wifes specifications(storage underneath) but whatever needs to be done to the top is flexible ie widening for turns and raising height or anything i need to do, so long as that storage area stays underneath im set
--EDIT--
i just noticed that you wanted to know what size loop would fit between wall and heater, answer is only a 15" radius and that is a no go as i plan to run a big boy or a challenger on this layout