Cobras were originally delivered with 3 different BB engines???
Really???? That's news to me.
I always understood that the 427 was delivered with the Side oiler initially then there was a run of 428 Police Interceptors then back to the 427 SO.
The oiling system in the 428 PI was a center oiler as I understand.
The SO has always been deemed the superior engine based on the cross bolted mains/stronger block and the higher revving ability due to it's shorter stroke and bigger bore. It also has a high nickel content block and stronger webbing.
The SO is the more desirable engine by far but cost drives most to opt for the 428. In fact it was cost that originally led SAI to switch to the 428 for a period of time. A number of original customers also returned their cars for the 427 SO to be installed based on performance. The 427SO is a nastier beast once the revs get up tach.
If you are not racing the motor to high revs or tracking it the 428 PI is a good strong torque monster that is a correct engine for a 427 Street car but not an SC or Comp spec car.
They look the same and sound the same. The 428 is easily a 1/3 or more lower in cost.
If you a nut for "correctness" and are doing a comp or SC it has to be a SO. If you are not a nut for correctness or are doing a street car a 428 is a great option due to price and performance it delivers. You won't have the bragging rights though and when they ask, and they always do "is that a 427" or "is that a side oiler" you'll have to say "no" if your honest. If that doesn't matter to you get then that's great.