The rebate portion of the combi is a z2 shear cutter with a spur on the top only for clean inside corners. It will also accept the small 40mm knives that are common in North America. The larger combi will not work with these small knives but does accept the larger "C" series knives. Bearings are available to match exactly as well as some offset if desired and custom ones can be made if you want an exact offset. Most of the features are discussed in this video where I compare the two:
https://youtu.be/LaJ7YgvDtLg
Additionally, this is a video where I start a custom kitchen door job and discuss the options for knives and overall approach using the combi:
https://youtu.be/MDgZ3r1LPg4
I'm not terribly familiar with the Harvey machines but I expect the large combi is too much for it. It's a serious piece of kit. The small combi is only in steel and will do everything the 96x55 block will do plus work as a rebate. However the geometry of the 96x55 block is designed to work perfectly when stacked with a 125mm rebate block to machine the sticking profile and rebate in one pass on doors and windows. There are certainly pros and cons to all the different options, feel free to ask any additional questions! I'm on the road a lot today, but I'm around
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