Snug fit, no clamps. on the plane with the ASP I use 7/64" tubing (At least, I measure about 2,7~2,8 mm), It is a snug but light fit. Has never slipped off in 5 years time, despite not using 1/8 brass tubing but 3 mm.

There really is no need for a tight fit, the pulling-off force acting on a 7/64" tubing acting on the Tygon because of the pressure is only in the order of magnitude of 0,005N or about half a gramme. A bit more than the weight of a hair.
I use a 2 oz craptrap, so even when the tank is full, there is always as a minimum that volume of 2 oz to be pressurized. I regularly fly the tank empty to a 20% reserve margin, and I notice zero difference between full and empty tank. Not even a noticable leaning out in steep climbs. In level flight, the tank is more or less level with the spraybar, in a steep climb (close to vertical) and on a near empty tank the fuel level is about 6" below the spraybar. Never noticed any problems with that in flight.

I really would suggest to simply install that engine in a plane, with a 10 oz Dubro tank and a craptrap of your liking, and start to fly it, to see whether what you think there is on the bench, actually is there in the air.
Don't get me wrong, I do not want to push you, but I get the feeling that you make too much out of the things you see. Sure, you had issues with heat soaking. They have been solved now. Maybe you have an issue with a too restricted pressure line. That can be solved too. Mind you, the occasional connection nipple with 2 mm internal bore is not the big problem. 8" of 2 mm tubing is. Gasses have viscosity too, believe it or not. My pressure line passes a muffler nipple (2 mm bore) a T-connection (2 mm bore. two connections on the craptrap and the connection on the fuel tank. But the tubing (all in all 8" of it) is that 2,77 mm internal diameter, and I do not have any issues with the pressure building up.
My throttle up slowdown is 1 sec, the throttle down slow down is zero. That works perfectly fine. Heck, the slowdown is not even set to 1 sec because of the throttle response... I did that mainly because it makes the thing sound like a much bigger engine. I have tested with 0,6 seconds and that worked perfectly fine too. The "sporty" sound does not fit the sedate aesthetics of that old BigLift... Rapid acceleration is overrated. it is not as important as many think.


Just go fly. You learn more about what works and what not by flying. Testbenches don't fly. It'll really be OK. Just keep your eyes and ears open the first few flights. I had to as well, and it all worked out. As it did with Dave, and many others. It will work out for you as well.