I showed Paul and his son (who is training to be a farrier) my Mayhew leaping head and asked if they could reshape it to look like the c. 1930's- 1940's one I had (I brought that one to show him what I meant). Paul's son took it and reshaped it for me and now it fits perfectly! I guess this is the first step in restoring my Mayhew.

The leaping head used to be too acutely bent for the size of my leg and the tip of it dug into it but now you can see that there is a proper hands width with the end of the horn pointing outwards and not digging into me!

The vet came out afterwards (it's been an expensive day) and had a look at Hattie's bump. He called it a Hydro-something or other (I cold just about make out the Hy and an O but the rest went over my head) and said basically that it was like capped hocks but on her wither. Having never dealt with capped hocks before, I asked him about it and he said that it was caused by something putting pressure there and then fluid built up there to protect it (which is why it felt squishy). He said it's like when horses get capped hock when they lie down on concrete floor stables that don't have that much bedding.
The vet said we could leave it or we could drain it and then inject cortisone into the bump but that he recommended the latter so that is what we did. Nothing came out when he tried to drain it, he said that there was very little liquid in it now (which explains why I was now able to feel her wither bone whereas before I couldn't so it looks like the liquid drained out) so the bump that remained was just scar tissue. He gave Hattie the cortisone injection and said that it should start to work in a couple of days.
The vet said that it may or may not come back and that if it did, then an injection wouldn't make much difference soooo, I'm just going to have to be extra careful with saddle fit and call Roger out probably a few times a year just to check Hattie's saddles as she changes shape with the seasons and workload.
I think if Hattie is healed in time for the Diamond Horse Show, I may just do it astride with our new high wither saddle and give her an extra month off for everything to heal 100% internally before side saddling again.