I have not done *this particular* engine swap, but I have done several others.
The short answer is that you can put the mounts wherever you want them. Since you are changing the engine and the trans, there are no hard datums for it.
If you can buy an off the shelf conversion mount kit for the engine, that will drive the location of the engine mounts (and should have instructions for where to put them). Once the engine mounts are located, the transmission mount location becomes a matter of measuring where the transmsission ends up when the engine is mounted.
If you are not buying an off the shelf kit, the answer becomes a bit more complicated. You still *can* put it wherever you want, but some locations will be easuer than others.
You want to be forward of the firewall, far enough back for your fan to clear the radiation, far enough to the passenger side to avoid the steering (or plan on rerouting the steering like some people do), high enough to clear the crossmember (or plan to move the crossmember), and low enough for the transmission to clear the tunnel in the cab (or plan to modify the tunnel).
My personal preference is to remove the hood, lower the engine and transmission down through the front and just hang it there for a bit while I inspect the clearance and look at how the trans hangs. From that, I can get a decent idea of where I want it to go. I can also see if I need to make changes on the vehicle side to have clearance for the exhaust and whatnot.
With a few hand measurements from the frame and firewall, I can make a rough mount to attach to the engine, set it back in place, tack-weld it on the frame side, unbolt/remove the engine, finish weld/reinforce the mount, put the whole assembly back in and bolt it up.
Once the engine is mounted, then I will fab up a trans mount wherever makes sense from how the trans hangs.
Note that the transmission is attached when I am fiddling on the engine side and I do use it to help position the engine to avoid mounting the engine in a way that precludes the trans being about to attach.
Other people almost certainly have other processes, but that is what has been working for me.
