I would go with stiffer springs all the way around before buying more expensive adjustable sway bars.
Also, there may be an issue with the MM swaybar fitting with Griggs TA/PHB, don't know, just saying they might interfere with each other.
You can move the 350# to the rear and run 450# in the front. It will be stiffer but you'll only have to buy one set of springs
FWIW, I ran 500# front and 350# rear for a while before getting the SLA upgrade. I didn't run a front sway bar with this combo. It was very tolerable in my opinion and no one htat rode in the car with me ever complained about how rough the ride was. I have a big KB blower on top of the engine up front so that's why the 500# front springs. It WAS too much though and I just pulled the swaybar to soften it back up some. I know the SLA was coming for Christmas so I wasn't wasting any more money on springs at the time.
I currently run 300# rear and 850# front with the SLA. I was told by Griggs the 850# fronts equal about 450# rate with a standard strut coilover. I also have their medium front bar one the middle setting.
My car will still push at the limit, but it takes a little more "pushing" before it starts to push now...lol
I got their WC LCA's on the way for the rear. I'll lose the rear sway bar with them so I'll probably up the rear springs back to 350# to make up for the swaybar being removed, plus a little to help balance the car a some more. And eventually I'll put the front bar on the softest setting. I have to make some of the spacers on the front bar smaller to get rid of some clearance issues.
That help any or did I just ramble about myself the whole time???