Ernie,
for me the rolling harrier is like an a slow roll, in that you feed in and out top rudder, and appropriate elevator input. It just takes a bit more 'cause you're keeping the nose higher. Its also (obviously) dependent on the plane, but I've found its way less than full deflection. Another consideration is that, just like in a slow roll, when you're going from, say knife edge to inverted, the elevator needed to keep the nose up effects heading between KE and inverted. So if you're doing a rolling harrier to the right (I practice them both ways) as you approach KE you feed in left rudder. Then as you leave KE heading to inverted you start feeding in down elevator the nose will want to veer to the left. So you hold the left rudder(which is in effect reversed when inverted) a little longer to keep the nose straight. In a really, long, slow roll you might even need a bit more than you did in KE.

Bla bla bla, the point I'm trying to make is practice slow rolls until the feeding in and out of controls and the corrections needed become second nature. Then, when you try rolling harriers you'll have a skill you can build on. Just use a bit more input.

AS far as throttle goes, I just sorta do that by feel, working it as needed.

I hope this helps. Best of luck!

Dave