RD-107 seems to have been used in the R7 missile. It says in the article for the missile that
1st stage: 4x jettisonable four-chamber RD-107 booster engines each with 2x vernier rocket engines plus 1x four-chamber RD-108 core engine with 4x vernier rocket engines.
So the RD 107 stage was used in quadruplets. So vernier engines existed on diametrically ...
I like the accepted answer, but it is a little abstract and I want to add to it with some visuals and more representative numbers. I created a crude launch sim and tracked the drag, gravity, and steering losses (for a sea level launch):
Edit: original version of this graph (and table) has some bad math on the steering losses, this has been fixed.
This shows ...
It's easy. All you need are:
a PhD in orbital mechanics
the physique of an Olympic athlete
a distinguished career as a test pilot
a fluent command of Russian
a great deal of luck
Let us know how it goes!
Edited to add: Galvanised by uhoh's comments, I actually googled this ("NASA astronaut requirements"). The official list is not entirely ...
Since this question was posted, plenty of exhaust plumes have been filmed from the ground giving a nice impression of the long term expansion behavior.
So, no, I wouldn't call it bulb shaped, but yes, the exhaust expands in ...