From a shop perspective...So what if an engine builder who IS competent tells someone much less knowledgeable "Sure, I can do that!"...takes your money and then blames something else as to why it blew up or didn't make the goal.
There's plenty of "pioneer" left in me but due to what I know...there's a limit to how far I'd try pushing a stock block because I don't have money to burn yet. I'd like to be able to enjoy it long enough to do what I want it to do. It's caution based on knowledge and experience. Perhaps there will be an aftermarket block capable of 4+ liters one day like the Buick GN guys have around.
Sounds like your in the business Intense.
I was too and I faced many customers with some pretty "interesting" ideas. I would listen then put forward my more rational recommendations. Most times the client would listen but, now and then one would come along that just wants to try it his way.
If the guy had the funds and realized the risks, I'd give it a shot. I'd often learn something along the way too. The shop owner as you described doesn't sound like you or any other reasonable builder out there. Sounds more like a liar and a thief.
Haven't you ever swam against the current and had a success? I sure have.