Does somebody ever heard of using a Speed Graphic as a shutter for a 8X10 barrel lens with the addition of the 8X10 bellow and camera back????

Specifically no, but the idea was. Folmer & Schwing did make a focal plane shutter for 5x7 and 8x10 view cameras.It attached between the camera and the camera back, extending the overall length by about 2".

Thornton Picard made several focal plane shutters of different sizes designed to go behind the lens, this made the shutter much smaller.

Deardorff made a shutter box that attached between the camera and the lensboard and used a Packard shutter. With the aid of a wood working shop and some mahogany you could create a Focal plane version of the same thing with a Speed Graphic body.

Thanks Les.So,it should work?The fact that the curtain is not right next to the film,as it is usually in the actual Speed Graphic(or any 35mm focal plane shutter for that matter)would not induce any blurr or irregularities in the image?

Nope. Thornton did it for years.