Monkey See-Monkey Do
Everything I have read or heard says a 6" rod for 383 sbc is the best way to go
Back in the mid 1950's Smokey Yunik discovered what was considered to him as the ideal rod length/stroke ratio. Most of the automotive engineers of the day agreed with him or listened to him.
At the time and in the style of racing competition he was in, there is little doubt that his findings were correct for his specific applications.
This fallacy of ideal rod length/stroke ratio was perpetuated by the many racing performance magazines and still is. Racers and even most engine builders believe what they see written in print in the magazines.
I like the philosphy of David Reher about this. "The connecting rod connects the piston to the crankshaft. That is it" Noting trick about rod lengths.
There is always a trade off with a short rod vs a long rod. Each one had advantages and each one has disadvantages. I build with both.
I like the idea of the piston configuration being far more important. Longer rods will allow shorter and lighter pistons, but at times you don't want a short piston.
I have built short rod 383 strokers, 5.565 rod, medium rod strokers, 5.700 rod and long rod strokers 6.00 rods in the 383 configurations. As far as horse power potential, I can't see any difference.
Do not be concerned about the having to use ring support rails. no biggie. Just prep and clean cylinder walls. with as clean of proceedures as possible and do a final clean with lacquer thinner or acetone followed with a light wipe of WD 40. Keep it all clean.
When you fire it up do not let the engine to idle at any low speeds and do not even let it idle long at higher speeds. Even idling at higher speeds, blip the throttle from time to time to load the rings some. After it runs for 30 minutes kill it change and check the oil filter and just let it all cool down completely. Check the valve adjustments, head bolt torque and fire it back up aftr it has fully coooled. This time you can let it idle a little lwer and begin to adjust tunings. eventually let it idle at as low of rpm as it can and adjust tunings for idle. Idle it back to where it will run. Let it all get cool again. Check all intake and header bolts and re-torque. Now you are ready to put it underr load either on the road or the dyno. Do not let it idle long. Try to keep it under a load with short bursts of full throttle. Check oil filter and change and check oil. Enjoy.
Ed