Main Bearing Clearancing

Depending on how big you are going to go, at 117 to 124 the stock HD cases get very thin at the mid connection point between the cylinders, so much so that the center bolt for the cases at that point has to be milled into a V shape and when you install it you have to get it lined up perfectly or the piston skirts will hit the bolt. Best bet is jims or sns cases if you are going really big.

Not that you can't bore out stock cases for a 124, you can, I did, but you need to know there are shortcomings as they were not designed for this size.

For a 103/106/107 this won't be an issue, and stock cases are fine.

Why wouldn't you just use the cases on the bike, if you're just going 103 to 107 it's a waste of money IMHO since you already have the cases, and the vin matches which to me is more important, especially if you are pulled over in sturgis, one of the things cops at rallies look for in the parking lots are mismatched vins.

They have crews that walk all the lots and streets at Daytona checking bikes all the time and finding stolen bikes...

the later flywheels and bearing assembly was changed by HD, it's reported
that the pinion shaft isn't as tight a spec as it used to be, so going gear drive
is harder with the later twin cams, but the new tensioners seem to be holding
up well so gear drive cams are not all the rage.

Early twins had some issues with the cam bearing selection, which HD changed, and the tensioners which some wore out in 20K others 40K but you do need to inspect them, if you havent' and you have a high mileage early TC you best pull the cam cover off and check them out before it's too late.

Yep you have to return the old ones, it's a control issue otherwise some crooks could just copy vins off bikes and order cases to make fake HD engines and bikes,

So what are you doing with it in order that someone might make an intelligent suggestion.