Red dot Tasco Optima 2000 help needed for a 5906 PC

[shootingisfun]

Would love to have a red dot on my 5906 PC 9mm. I purchased a Tasco Optima mount for a 59. The mounting plate fits the profile of the slide great however the dovetail piece does not fit and modifying it doesn't seem like a great idea as there isn't much metal to it.

I really like the mounting plate as it transitions nicely from the slide to the red dot but I need help figuring out how to get a correct rear sight adapter piece.

Does anyone have a different Tasco Optima 2000 mount that may have a more appropriate rear sight adapter piece? I could order one and modify it to fit.

Next question, a few weeks ago I was searching for a mounting plate and I came across a website that sold adapter plates for various Kensight, LPA cuts. I swore I saved it but now I can not find it. Does anyone know who offers that?

Also does anyone know what the piece of metal is for on the left hand side?

Thanks