I know what you mean about losing interest. I've got three machines in various states from torn down to partially assembled. That's in addition to routine maintenance which seems to be ongoing on the others in the fleet. I'm building a new work shop as well so everything is here and here including tools, welders, etc., and nothing is where I need it.
As big as the machine is, its amazing how much space can be taken up. Been there and done that.
I think you are still in line for a top notch amphib here. I've always liked how the t20 performed, especially with split shifters. The Avenger is really an over-engineered vehicle anyway. I may do one one of these days myself, and keep thinking about single #80 chain throughout, and maybe a 33 to 35 hp engine.