the 6.0l is the same bellhousing pattern as any other chevy minus one bolt hole that isn't tapped on the 6.0 block and the h55 is the same bolt pattern as a 4 speed box so all you need is a chevy to toyo bellhousing or adaptor plate, your h55 will have the long fine spline input shaft if it came off a 3b diesel so you'll need to change the input shaft to a short course spline or make sure you get a deeper bellhousing for the longer inputshaft. when we did my 6.0 swap we put an ls1 flywheel on the 6.0 and reused my old 350 to h55 dellow bellhousing it all bolted up fine