Update - Prof Google provided advice on getting the top cap off and a combination on wd40, a better tool and undoing the stem clamp bolts and turning the steerer a bit first did the trick.
I've flipped the stem and done a new diy bike fit (the saddle needed moving slightly) and plan to do a 2 or 3 hour ride in the morning to see how things feel. I may not have the bars in the right position and may need to rotate them a bit one way or another or may even still need to shorten the stem but will know more tomorrow. Doing 100 mile sportive in 3 weeks so I want it to be just right. Thanks for advice.