I do know a lot of people use hockey pucks for body lifts on their 4x4s. Not sure if that is a good thing or not, but plenty of people use 'em.
I'd venture to say that if they are indeed stiff enough to use as body/frame spacers, they should be fine for engine mounts if you want to go that way. Maybe some others have more insight on hockey pucks....I've never even touched one let alone inspected it's properties. FWIW, the 4.6 seems to be one smoooth running motor with proper tune. Solid mounts shouldn't be a problem even in DD status.
But spose I should ask this: Why do you feel you need solid mounts for your car?
Lots of torque? Worn out stock mounts?
Addressing those two possible scenarios, I can say that the cars I've had that I felt needed solid mounts only received a solid mount on the driver's side anyway; the rest stayed with stock specs and no more trouble came from that kind of setup. For instance, I used to break the driver's side (stock) motor mount on my 78 Cutlass every weekend I went out to play. Had to hammer out the dents in the hood that resulted from the motor mount breaking on the holeshot more times than should be legally allowed.....not to mention having to baby the thing back home with tail firmly tucked between legs.
What I ended up doing (after being told by the local salvage yard that the one they are selling me this time was the very last available mount they had for my car) was to make that one solid. That problem was then solved once and for all.
The engine stayed put, the remaining stock mounts on pass. side and tranny still allowed my teeth to stay put, and Camaros were sent to go lie down by their dish and keep quiet.
Delete my account.