Toroidal Bore, Revisited

I am now tasked with designing and building a tool to produce a
Toroidal chamber inside of a bore. I mentioned this a few weeks ago to
the group but now it's for real. It is really a unique shape, I haven't
been able to find any ready made tool that can do the job.
I plan on making basically a concave radius cutter on the end of a
massive boring bar. Actuated manually (for now) with a worm gear drive.

Does anyone have any experience with making their own radius
cutter? Advice or suggestions?
CNC profiling is really not an option. After you do all the math
for the entry and plunge depths, the tool ends up being too long and
skinny to get a good surface finish.

Wish me luck, I will post pictures when it is done, or I will post my
resume.

"Matters of great concern shall be treated lightly"