Txmustangflyer

Now, I'm not going to try and say its this or that, but you, yourself, questioned the distance from the bell to the turbine.

You are the builder, they, the manufacturer. If you questioned the distance did you a. Call and verify, or b, adjust to what you thought it should be? According to your post, you did not do the latter.
The measurement could have been a simple typo, not caught, before printing.
Have you contacted CARF, at all, about the incident.
To my knowledge, they do support their products, but, some common sense also has to be used.

Its no different if you mount an engine for a prop driven plane, if the spinner is too close to the cowl and it rubs, you going to leave it?
They cannot account for, in their build manual, every single power plant that could possibly be put in a plane. I know of, at least 6 different companies that make rc turbines off the top of my head, at varous diameter, thrust, and weight. To do so would require months of very expensive testing of each and every possibility.
You followed the manual, I don't fault you for that, but when that red flag went up, further research to be sure needed to be done. The lack of it almost cost you thousands of dollars. Right now, at this moment, a phone call to CARF with stills from your video, as well as pictures of the turbine spacing you had would go a long way to getting parts replaced by CARF AND making sure that the manual is updated so it doesn't happen to others.

I'm not going to brow beat it, but CARF is only, partly, to blame.

Our hobby is costly, sometimes dangerous, any red flag, such as your "that can't be right" moment should stop progress until further information from the manufacturer clarifies it and either resolves the doubt, or fixes the problem.

I have, yet, to build a turbine. Its on the to do list, but I have had a few of those moments on the current project and, every time, the tools get set down and phone calls and emails go out until I am sure of the right procedure, measurements, amp loads, etc. It moves no further if there is any doubt.

We are as responsible for building a good plane thats as safe as we can make it, yes, manufacturers SHOULD shoulder some of that responsibity, but it is, ultimately our ball, not theirs. Had they shipped you a completed aircraft, everything installed so all you had to do was fire up the reciever and bind, then its all on them.

This, is not that. They design a plane, pick an engine and design the included systems based on engine, servos, linkages, weight and balance.

One thing I have noticed in 20 years, is that most aircraft manuals are based on one, maybe two, engine choices out of many.
Might be worth the time to drop an email and ask which they used prior to clicking buy. The engine they used in prototype may have required that spacing. Yours requires more..that simple.

Its my understanding, that each turbine manufacturer has a recommended spacing for each of their engines. IMO, unknowledgeable as it is, that would be the measurement to use, no matter the bell material. The guys that designed and built ypur turbine know exactly what spacing would be needed based on exhaust temp at WOT to keep from melting the bell and charbroiling the aircraft. It wouldn't have mattered what CARF had in the manual, at that point and we wouldn't be reading about a fire, but a maiden. The reason for the spacing, in part, is to let the exhaust gasses cool a bit before hitting the tube and bell. I imagine diesel runs cooler than jet a, kerosene somewhere in between.
I'll be honest with you, other than finding rough linkage lengths, throws, and cg...other than a "how did they do it" because I'm not coming up with it is about all the creedence I give to an ARF instruction manual. Everything is done per the component manufacturer recommendations for install. Everything.
exceptions to that, anything thats hinged.

There were multiple ways to resolve your concern. 1. Most difficult: trim the tube down and space the bell back as much as you could, fashion new mounts.
2. Slide turbine forward and redrill the rails.
3. Combination of both.

These things are up to you, as the builder, not CARF

My .02