Toro Dingo TX425 gas, engine replacement hydraulic fluid and tips

I'm installing a new replacement Kohler gas engine in my 2005 Toro Dingo. I have the Toro Service manual pdf but it does not tell me to drain the hydraulic fluid out. Seems like something I should do. Anyone a Toro Dingo mechanic or have experience directly with this? I prefer not to drain it out if I don't have too. Also it says to cap plugs, but I plan on using yellow rubber plug inserts that you push in and twist. And suggestions or tips on the whole process?

It's easy enough if you're mechanically inclined. You'll need a few crows foot wrenches. Yes I drained the hydraulic oil to replace the engine as it was almost due anyways and made it easier. Support the arms when you do start working on the hydraulics

I did finish the replacement work. I did not drain the hydraulic fluid because it had less than 200 hours on it. However, I did install a new hydraulic filter, idler pulley, Muffler heat shield, new oil drain line, and re-painted the battery holder. Most of the replacement wasn't too bad. I had a pdf file of the parts diagram and the full service manual which is a pretty good step by step. I did have some issues with the following. I used yellow tapered plugs (push in and twist) for all the hydraulic lines. The plugs I had did not work well and constantly fell out. I ended up using plastic bags and zip ties. Plastic caps would have been best. A lot of the hydraulic fittings are over 1" in size and hard to access to get enough torque to loosen. The job isn't real hard, just a lot of steps to get out, and a lot of steps to put in. I also cleaned and inspected everything. Was going to clean out the fuel tank, but in the end, never did that. Dealer price would have been in the $6000-$7000 plus tax price and more with cleaning and extra parts install, but for me to purchase the engine and other parts was probably just under $3000.