A TH-75 is definitely overkill for a plane designed to weigh 4 pounds.

A 'typical' ball bearing .46 weighs around 17 ounces with muffler. The TH-75 weighs 23 ounces with muffler.

You could modify the fuselage slightly and mount the servos near the tail to offset some of the engine weight. You might also need to mount the receiver battery behind the wing. Ground clearance for a big prop might be an issue.

As long as you can balance the plane, without making it grossly overweight, I guess you're ok.

As they say, you can always throttle back.