Bob,
It's not difficult, I was using a pathetic little half-pint blowlamp, and being far too impatient. I did want to mention the potential runaway hazard, which I guess has reduced the survival rate of these engines. I gather many S-type owners have a notable incident with the engine in the early days of owning it :-).
A few minutes with a gas torch like plumbers use, or a decent size blowlamp burning properly should heat it up quite sufficiently. Aim at the hot-bulb rather than the tube, at the base of the hot-tube. The tube will start changing colour towards red when you're hot enough, sometimes difficult to see in stong daylight.
Also you can pump in a shot of fuel with the half compression c*ck open and move the engine through TDC. If it's hot enough, smoke should come out through the half compression c*ck.
The help of Roland Craven and Philip Thornton-Evison much be acknowledged at this point, Philip put me on to the previous owner of my 5hp engine, and he and Roland answered all of my queries. They've both forgotten more about these engines than I will ever remember ;-).
Regards, Arthur G