I'm afraid I'll mislead you here, and Geo is like an encyclopedia, but I had my wooden dash on my 4A made by Randy Keller in Santa Ana. He's excellent. However, the chrome bezels definitely mounted from the front with his work. I was instructed to use a small round grinding stone to enlarge the hole in the steel backing piece so I could get the plastic housing right up against the back of the wood dash. Then, the bezel screwed in from the front.
Keller had told me that when he makes the wooden dashes, he prefers the bezels to be mounted that way. On a TR4, I'm assuming it must work differently due to the original steel dash, and Geo would know best.
Below is the picture of my dash and you can see the chrome bezel mounted from the front. Keller wants his that way, and among the reasons is to "show off" the chrome.