Um, why would I be upset answering questions and explaining things? It's fun!
Not sure why you find it unlikely that a large engine was tested on a large aircraft. The ram jets had huge thrust and needed lots of fuel.
The high drag , twin tail and sturdiness of the surplus obsolete Dornier made it the ideal expendable test bed for potentially self-destructing experimental engine. Much wiser than testing on a rare and valuable craft like an Arado or Me262.
Yes, a Dornier 17 goes 500km or so. With a ramjet it goes 650+ km'hr
If you understand the aerodynamic cube rule, that to double an aircraft's speed, the drag goes up by the square and the power goes up by the cube, or in other words to double your airspeed you need 8 times the power, such a large percentage increase in speed of a highly draggy aircraft at the low end of the ramjets operating speed range is highly significant. The ramjets were mighty powerful and they weren't even anywhere near their efficient speed range yet.
As a result of the succesful tests, special versions of the engines were planned to be trialed on Me262s and other craft.

Yup, the Lorin ramjets were indeed centre mounted over the back of the Dorniers.
The larger one shown is the Skoda Kauber, the smaller one the Sänger.






OK wind tunnels:
Allies: In June 1942 a 9inch diameter supersonic wind tunnel went into operation at the Langley Aeronautical Laboratory capable of Mach 2.5 airspeeds. By late 1945 an 8 by 6ft diameter tunnel capable of mach 2 airspeeds was in operation based on captured German tunnels.

Germany: supersonic wind tunnels were operational in Peenemünde, Aachen university, Friedrichhafen.
Dr Rudolf Herman designed the Mach 3.3 10cm x10cm tunnel at Aachen technical university, operational in 1937.
By 1938, two 40cm x 40cm mach 2.5 tunnels operated in Peenemünde by Dr Herman and Dr Kerzweg. After operation crossbow in 1943, the Tunnels survived unscathed but were transported by rail to Kochel in Bavaria.
Post war they were moved to White Oak MD along with 12 German technicians. the German scientists contructed the 16ft by 16ft tunnel and continued use of the Peenemünde tunnels and were all were used to design numerous American aerospace devices including the space shuttle.

Deltas can fly at extremely high angles of attack as the wing becomes engulfed by a massive bound vortex spiralling off the leading edge of each wing where flow separation takes pace. It is this energetic bound vortex that provides much of the lift at this AOA and represents what would otherwise be a fully stalled condition on a conventional wing. The extreme angle of attack possible by deltas is also a high drag state and deltas in combat lose velocity rapidly in high g turns without massive applications of power.
Your comment about if you push the nose down a delta will crash is not correct. Reducing the AOA will reduce lift somewhat but that is how lift is modulated. It doesn't mean that the delta will fall out of the sky.
Delta wings are not "intended for use at supersonic speeds".
They are a practical platform that incorporates a large wing area in a small wingspan and extremely strong structure. Some Deltas are good for supersonic speed , some are never intended to go supersonic.

Some deltas are capable of supersonic speed but the majority of deltas in reality spend most of their time subsonic.
Airforces usually don't fly their supersonic capable aircraft at supersonic speed for any length of time due to the enormous energy cost and noise.
The delta winged A4 skyhawk fighter for instance had a max speed of 1077km'hr and had decades of use. The delta wing Avro Vulcan bomber too did not fly supersonic.