headset replacement

I cannot believe that two bike shops couldn't remove that crown race! I think you should name and shame them - pathetic. The video link you posted is all you need to do to remove it - then find another (decent) bike shop to install the new race. However, before doing this I would 'suck it and see' - assemble with the current race and test ride.

A quick and easy way to fit a new race, is get a piece of plumbing pipe. Run a saw through the diameter to create a 2" slot. Heat up the new race in the oven, drop it quickly onto tube upend forks and with plumbing tube bash it into place.

Getting old race off , I've found a dremel to cut through most it then gently ease off

The bike shops you visited were being lazy I think. Those races are a pain to remove, as you have to work a blade or the like under it to get an initial small gap. Once you have it lifted by even a tiny amount, a Park Crown Race Puller will get it off.

I grant you, it takes half an hour rather than 5 minutes, but it is easily do-able. If you live near Monmouth, I'd happily sort it out for you.

With regard to whether to leave the old one on, it depends on what the bearing angle of the bearing is and if that is the same as the crown race. If it isn't then the bearing will be getting a point load on it that will inevitably reduce its service life.

I'm not sure what you mean by a small log. I'm guessing at lip? The base of the old race looks slightly smaller than the new one. If so, its not a huge issue and you can ignore it.

Obviously, I can't be 100% sure but looking at the photos, I think it'll be fine to use the existing race.

One last test...

Slide the new lower bearing on and compare it to the look and feel of the old one when in position. Push down on the bearing and move it side to side a bit. If it has play between the crown race and the bearing you'll need to try something else... Either reusing the old headset with new bearings or finding someone to get that race off for you.

If there's no play,  and the bearing only wants to turn rather than wobble then you are good to go. Just swap all the old parts except the crown race.

To be honest, unless you have the right tools, crown race fitting and removal can be a real pain.

Does the bearing sit nicely on the old race on the down tube?
I would dry assembly and check for smooth movement without any catching. If that works disassemble and grease mating surfaces.

So it's an integrated crown race?

Like I said above, compare the numbers on the old bearings with the FSA ones.

If they're the same (which is highly possible) just fit them. If they look completely different, you'll need to hunt for replacements on the net and return the FSA headset.

This is the point where we start asking for photos so we can help more...

As previous poster has suggested, get the LBS to change it, all the parts will be made to fit together, for a start the sealing will work better.

Sealed bearing, just replace, with a smear of grease on the mating surfaces.

Sealed or open bearings carriers?  Unless badly corroded, dont bother, clean and slap loads of thick grease on re-assembly.  It will last years, there is very little rotation movement to worry about, just the right amount of preload to ensure no free play.

You should replace the crown race as it may not be the same profile as the one with the new headset. If your new crown race has a split in it then it is a really simple job to install, if not, then a quick trip to the LBS will get it done (30 second job). Removing the old one is simple too. Lots of vids on the 'net (recommend Park Tools stuff).