I've got the straight Highland - bought it two summers ago on a whim because I saw a sale I couldn't refuse. I like it a lot but I've done a lot of mods.
I think of the COS's, defined by less than quarter inch steel, OKJ is probably the best.
Having said that, Jirby recommends sticking with what you have, saving your money and getting a Mill Scale 94. :-)
I thought the reverse flow was switchable without having to buy a 2nd stack. Can't one just loosen a screw and move the stack to the conventional side?
I like the idea of the reverse flow, but for some reason, the straight Highland is rated higher on
Amazon than the reverse. Why? I don't know. One thing that bugs me about the reverse flow is that the stack is on the side.
Re the firebox, the V shape grate is an improvement over the stock set up, but a charcoal basket is a vast improvement over the V shape. See Smoke Trails BBQ on youtube.
My highland cooks very nicely with even temps from right to left, but it took some mods to get there.
Good luck