The statement in the comment that you may have lost some parts is helpful in figuring out what happened here.
You need to determine two target dimensions: the distance between the drive-side flange and the drive-side locknut face (R), and the distance between the non-drive flange and the non-drive locknut face (L).
Lacking other information about what R was initially, choose a distance for it such that the chain clears the inside of the frame with the freewheel mounted by 3-4mm. Put it together and make sure you're happy with how that side looks. Then determine your OLD (same number as your frame spacing), and subtract from that number the distance between the drive-side locknut face and the non-drive cone outer face. Then subtract the thickness of the non-drive side locknut you're using. The remainder is the thickness of your ideal non-drive side spacer stack. Put that in and your L value is perfect. Center the axle protrusion with the hub in that configuration and dish the wheel.
The 3-4mm above is a fudge factor that most freewheel hubs more or less conform to. It also represents the smallest practical clearance gap. By using the smallest value practical there, the wheel is at its strongest. Using 3-4mm as a guideline will probably lead to a drive-side spacer stack dimension that is close to whatever it was originally, but not exact. If it's not exact, you need to redish the wheel. If you want to do this in a way that avoids the need to correct the dish, you'll have to put the hub together and check the dish until you've inferred what the drive side spacer stack dimension was initially.
The 135mm number you mention in the comments as the outer dropout dimension is not material to any part of this.
The 132mm number you mention in the comments is suspect. Either it and/or the 135 number are incorrect, since the dropouts of the bike in the picture are not 1.5mm each. Your frame likely was made with a target spacing (the internal dimension) of 126, 130, or 135. That part doesn't really matter; just get an accurate measurement of it and build up the hub OLD to match. On an aluminum frame, it is unacceptable to have significant difference between the hub OLD and the frame spacing. They're tolerant of 1-2mm, but with what you're doing there's no reason it shouldn't be zero.
The part you identify as an external lock nut is usually called an axle nut.