I haven't built either of the Heller 74 kits. I bought one of them about 40 years ago, but the combination of the one-log hull, the flat decks, the too-wide deck planks, and the copper all the way to the wales sent it to the bottom of my stash. When I moved from Ohio to Virginia, I consigned quite a few kits to a local hobby shop. I guess it sold.
One approach to the hull plank problem would be simply to scrape off the "wood grain" and leave it at that. Plenty of modelers prefer the look of a smooth hull surface.
If I were determined to scribe the edges of the planks, I'd first try doing it with a small pair of dividers. Follow the adjacent wale with one point of the dividers, and scribe with the other.
Another approach would be to lay down several layers of thin striping tape along the line you want to scribe, and use the tape as a guide for your scriber.
There were differences between French and British rigging practice; whether those differences are worth the trouble in a 1/150-scale model is up to the modeler.
The rigging diagrams in the Diana book probably would be about 75 percent for a French 74 of 30 years later. A better source would be the "Anatomy of the Ship" volume about HMS Bellona (a British 74).
Incidentally, one of the nice features of the Heller 74 kits is that they offer the choice between lateen-rigged mizzen sails or gaff-and-boom-rigged mizzen sail. That's correct for the period. During the American Revolution ships of all navies might be rigged either way.
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