The Bosch weights 8.36 pounds according to the bosch tools site. I tried to see what a C3D spindle weights but could not find that However a Huanyang Water Cooled CNC Spindle weights 12.65 pounds plus the water for cooling. So the weight may not be a problem but the center of gravity might. With the 3.5" spindle of a bosch that is 88.9 MM diameter and although that is not much more than an 80MM spindle it is much farther to the center than a trim router 66/69MM. The other problem may be finding a mount to fit the Shapeoko on the Z-Plus/HDZ. You could make one with the Pro XXL but finding a commercial available and drilling holes to fit the Z-Plus/HDZ might be cheaper. The Bosch is a 2.25 HP which is almost double a trim router C3D/Makita. The Huanyang is 3 HP so there is not too much difference in HP.
My question is why reinvent the wheel when you can buy off the shelf products and get the mount from C3D to fit most after market 80MM spindles. If you need increased HP why over complicate. The C3D air cooled spindle is plug and play although it is $750.00 you would have a warranty from a reputable company and the spindle would be supported.
The Chinese spindles offer almost no support. You only support might be here on the forum for spindles that someone has already invented that wheel. Save yourself aggravation and time and buy something off the shelf.