The Lyman manual indicates a length of 1.590" but length not listed for Oregon.
Take a good look at your Lyman manual. Where is that COAL listed? Is it listed in the data for that 180gr bullet? Are there any different COALs listed with different bullets??
1.590" is the industry standard max loaded length for the .357 Magnum cartridge, no matter what bullet is used.
Industry standard max length is set to allow the ammo to function through every gun made to industry standard for that caliber.
And, its not a "dare not exceed" length, tis a "should not or you MIGHT have function issues" length.
In other words, if you load longer than the max standard, your bullet might stick out the front of the cylinder (not good) or might not feed from the magazine (also not good) but if you load to industry standard length or less, you should not have those issues.
Next point, when you do have data that gives a certain COAL with a certain bullet (and it will be 1.590" or less, almost always less) Is that the length the data creator is recommending? OR, is it simply the result they GOT when seating to a given point (such as seating to the crimp groove)???
An easily seen example of this is some rifle bullets. Take a .30 cal 150gr spitzer and a 150gr flat point or round nose (such as a .30-30 bullet. Seat them to identical depth in the case, so there is no difference at all in powder space volume. There WILL BE a difference in the COAL. The flat point, will be shorter.
The difference is due to the difference is the shape and length of the bullet NOSE, the part outside the case. This principle applies to pistol bullets as well. its just a little more difficult to easily see...
Just for comparison, I grabbed an old (1970) Lyman manual. It doesn't even list a 180gr cast bullet. But it DOES list a 195gr cast bullet #358430 (#2 alloy). Test gun was a S&W model 27. 2400 powder, starting load 9.5gr, max 11.0gr
So, I would say it should be ok to load your Oregon Trail bullet with the Lyman data, PROVIDED you do the recommended and smart thing, start low and work up to the listed load, carefully, in small steps watching for anything indicating excess pressure. DO NOT START AT LISTED MAX, EVER.
Most gun and ammo combinations fall in the middle of the bell curve. BUT extremes at each end do exist, and there is no way to know if YOUR gun and your ammo is at either extreme end, until you shoot it.
IF your gun/ammo combination is one of the rare ones, and at the low end of the range, you might not be able to reach the listed load in the data before getting pressure issues. Starting low, and working up in small steps allows you to see if those issues happen and stop when they do. Even if you haven't reached the listed data charge weigh, you stop.
Point here is that published data and industry standards are guidelines (and good ones!!) but are set well below actual safety boundaries. IF you exceed the guidelines, you're off the map and into the part that says "there be dragons here!"
So you must tread carefully, so a dragon doesn't eat you. People have done it successfully, and people have been "eaten".
Best practice, stay on the map!