57 Chevy 235 timing

[juker17]

Just got a 57 chevy with a 235 c.i. six cylinder. Trying to figure out how to check the timing on this. Ive read a few old threads and still have some questions. First thing Ive noticed is that I can grab my distributor cap and move it, about an inch or so, it is spring loaded and will return to its original position. It is hooked up to the vacuum advance assembly, I can see it moving as I twist the distributor cap. Should I be able to move this by hand? Shouldnt it be clamped down in a certain position? The other question I have is concerning the octane selector. I have the knob near the bottom of the distributor cap, but I dont see the guage as shown in the service manual. The one that has a 0 setting on it and an A for advance and R for retard. Its missing. Will I need it? Isnt the octane rating for gas back in 57 so much different than todays gas that it wont matter? Thanks for any help. Jim