For many years, reloaders substituted similar bullets when following loading details in manuals. In fact, many/most manuals listed bullets in general terms, like "200 grain lead", then gave powder charges. Other details like brand of brass or primers was not listed. As companies got more sophisticated pressure-testing equipment, they discovered that those kind of details mattered. As mentioned, the overall length is less of an issue than the depth that the bullet seats into the case and the amount of surface area that makes contact with the barrel (creating friction/resistance). Of course bullet weight is also a major factor.
Still, and take this for what it's worth, I would feel comfortable substituting very similar bullets like the two cast lead bullets that you mentioned. OF COURSE, you will want to start with lower powder charges and gradually work up, following the safe loading procedures described in your Lyman manual. You might not want to approach maximum loads too closely with those substitutions either. As mentioned, jacketed bullets and lead bullets do not compare and cannot be easily substituted. You also cannot generally substitute powder types and should follow load data from reliable sources.
On that last topic, answers that you get from the internet are often not to be considered "reliable sources". As far as you know, I'm just a 10 year old kid making this stuff up or a foreign agent with a nefarious plan to destroy America by giving bad handloading advice. Again, take what I've said for what it is worth and study your manual, and not just load data--carefully read the loading procedures that are included. Use caution and enjoy yourself. I find loading ammunition to be nearly as enjoyable as unloading ammunition. Nearly.
CC Griff