Hi,
I’m responding as some jargon needs to be massaged into play here, if you are thinking of rebuilding an engine from salvaged parts.
Have you done anything like this before?

Planetman is correct about having the journal bores align bored or in-line bored in my language.

At least have them swept for roundness of which could take as much time as to bore them straight.

It’s Depending on amount of time on your hands or money as an option.
Otherwise you are looking at using a lot of Plastigage®.
It squish-able material that is measured with its provide spread chart after bolting things.
It checks clearances around shafts or for Babbitt insert(s) fitting.
It determines what inserts you will need to purchase.
Inserts are rolled into various thicknesses as sets.
That works with line boring all journals to the same diameter.
I don’t know about only buying one over the counter but they are packaged and sized.
I have never rebuilt an engine in totality or from pieces that you are proposing for that matter.

You are talking about the journals in between the cylinders and not connecting rod caps.
Using the term six or eight shifts my thinking and that’s like shifting gears without using a clutch.
I felt a clash. 😬

When referencing the crankshafts number of caps one should account for multiple cylinders that will require an additional journal so the number always ends up odd.
Of course if it’s an odd number of cylinder 1,3,5, engine then you get an even number of caps.
Volvos four cylinder is considered a five bolt main.
Years ago I saw it advertised as a strong feature by marketing.
Here is another case of one or a zero times a number is twisted fact.

Now since we discuss differences the caps on the outboard ends can be made differently. Some support thrust bearings recesses, oil slingers and so on to a point maybe to achieve a shorter engine by one journal.
Maybe that’s been done by somebody trying to get an advantage.
Oh, the games engineering can tease themselves with. 🤫

Just like rod caps are mated to their respective rod bodies as a set and the weight of the assemblies are closely matched into sets for each engine for better balance.
Journals get the same care with respective to a Block to their split line.
They do not spin so their weight is not a dynamic one.

During machining a block they will have their caps and hardware set, installed, over a split line made on both parts beforehand.
The caps are assembled in a numbered order in one direction of the engine during machining.
Same for overhead cams in the head.

Today’s rod are “sintered” rods where the cap is broken off or apart it’s after the rod body is machined.
The breakage seam then becomes its very own matching piece of split line.

Happy hunting and matching. 🤞

Phil