Forget trying to sniff each cylinder, takes way too much time for the small gain, plus it gets too complicated.
It seems you have a good handle on the hp figure too. It's only a number, don't dwell on that. I find I can easily feel a four hp increase. You're way over that and you'll be happy with the increase.
Synching carbs- even the dials. It'll be obvious when you're close. It takes some fiddling to button it up after as settings can change. Be patient and use a large fan in front of the engine to move some air over it.
I'm not going to re-read so some things have already been mentioned. Stock ign settings will likely make it happy. If you want to try a couple degrees either side of stock, do that first before carburetion. Try to mark your existing spot so you can easily get it back there then approx. 1/16" rotation clockwise of the plate retards timing by +-2 degrees or vise versa. If you are adventurous and move it around to no avail then reset to the original mark for carb tuning. You can re-test with a strobe later. Flat top pistons and small 500 chambers don't need much ignition lead, but with 1:10CR or so stock settings may be best.
A dyno will help find the mainjet with WOT pulls. This is where you should focus. With a sniffer get that right and be happy. For the street though you may need to do some work on your own as far as needle settings & pilot selection. Just for giggles try raising the needle by 1 clip. I have found even with increased vacuum from a fresh top end I always need a larger pilot jet for that "off idle" bog we get pulling away from a stop. Try the air screws first but any more than 1 turn from stock settings will require a jet change, usually larger for me. I like to use tapered jet reamers, others have jet drills, but if you can find the right size pilot so much the better.
Calculating CR....Swept volume +combustion chamber volume, divided by that volume.
Swept volume =finished cylinder bore x bore x stroke (50.6) x 0.7854 divided by 1000 =cc's
Chamber volume includes
1) chamber (500/550 is 13cc's) plus 2) head gasket (calculate this the same as cylinder swept vol.) plus 3) piston net dome (may be 0 with yours) plus 4) piston above or below deck value (unless it's even with the deck) plus 5) piston compression shoulder to top of 1st ring. This is a small value but for accuracy...
For example 605 kit is 61.5mm? Lets figure you asked for 0.001" piston clearance (0.025mm) so swept volume is 150.434cc
chamber volume is 13cc
head gasket, lets say stock thickness with a 62mm bore?? for 3.2cc
piston dome, lets say "0" for arguments sake.
let's also say 0.010" below deck....just guessing here. 0.74cc
comp shoulder to top ring (usually 3mm??) another guess at 0.295cc for a total volume of 17.235cc
150.434 + 17.235 divided by 17.235 = CR 9.7
You can plug in your exact figures if you have them.
Good luck!