You know what you're doing. One significant variable for you is coating vs traditional lube. If coating does not work, trying the same bullet in traditional lube version is an option. With the latter, some vendors offer a diameter option like .357, .358, or .359. Regarding shape, round nose flat point and lbt profiles have excellent accuracy reputations.
Marlin rifles traditionally had micro-groove rifling which did not lend itself to cast bullet load development. I urge you to verify your gun's rifling. If you later try bullets with traditional lube, consider ordering .359 diameter. If these do not do well, you can run them through an inexpensive Lee lead bullet size die to reduce diameter to .358. My guess is that .359 is a better choice. The reason is that your Marlin rifle and Ruger revolver will most likely have larger bore diameters.
Commercial cast bullets are usually too hard. Lube types vary. Softer lube is better than hard. Commercial casters tend to use hard lubes so that the lube remains within lube grooves. The easy way out for you is to buy cowboy action bullets cast of softer alloy. With these develop accurate .38 velocity loads. This method facilitates the easiest way to select a suitable bullet and accurate load. You may find that these same bullets will do well for faster velocities. If not, you have determined essential information.
If your lubed bullets are leading, try this. Buy a bottle of Lee Alox type lube and dilute it with mineral spirits. Mix 50/50 and dip the regular lubed bullet in this. Let dry and load. This mix can be further diluted and then applied with a shake/bake method.
If your rifle will not shoot jacketed bullets accurately, neither will it do well with cast bullets.