My hob is currently fitted with a flexible hose. I understand
that this is fine so long as the hose hangs unstrained and doesn't
come into contact with anything hot - I think 70 degC was the figure.

I need to move the hob, and will then be unable to use the hose without
inserting a M-F elbow between the hose and the hob. Am I right in
thinking that I want a malleable iron MF BSP 1/2" 90deg,

for example part 6377 on BES?

I also noted the existence of a restrictor, apparently specifically for
hobs. The existing installation doesn't have one of these. Should this
concern me?

For the avoidance of doubt, I'm not planning on major gas works. I'm
paying someone to install a new boiler for me. But I do have experience
with water plumbing, and am happy making solder and compression
joints. I also understand that the new joins will have to be checked very
carefully for leaks. I know that I need to use a suitable jointing compound.
I don't see how the insertion of a simple join can be beyond me. But I
am very willing to listen if someone points out issues or dangers that I
have
not considered.

If anyone can suggest some good reading material on the theory and practice
of gas, I'd be very grateful. I have a degree in Engineering, so it need not
be that basic.

Ben