To butterfly a pig you split him down the belly, and open him up flat. That takes breaking the rib bones on one side. Then you stick a couple of skewers through him -- usually rebar to hold him that way, wire his legs to the rebar, then wire another piece of rebar across those pieces, to hold them together and form a tree. Finally, you wrap the whoe pig in light wire mesh fenching to keep him together and make him easy to turn. When you're ready to turn and/or flip him, you use the rebar as handles.
Racer style means you let him keep his shape, and arrange him as though he were crouched. His upper legs point forward, but his lower legs and hooves point back in the same direction as the tail. If you're going to stuff the pig at all, even aromatics for roasting, peaches and onions for instance, go racer. Again, you wrap the pig in wire mesh, and wire it together, so you can pick him up and turn him. Again, you wrap the pig in wire mesh, and wire it together, so you can pick him up and turn him. If it's a big pig, you wire him to a rebar tree (as described) to make turning a little easier. You're not going to flip a racer style pig -- but that's not an issue in a smoker, only open pit or cochon au lait.
Semi-racer is racer style, but the rear legs and hams are extended backwards. Beginners tend to find that this cooks most evenly -- but I think it loses its utility once you get over 60# or so. Again with the wire and rebar, if you plan on turning the pig. Turning probably isn't absolutely necessary in a very large, and well tuned pit. I just haven't cooked a pig in that pit, yet.
I've found it easiest to carry a racer style pig to the table, by putting him on a custom made stretcher made from two 2x12s, cut and nailed together for the purpose, and covered with an enormous amount of heavy duty foil. You can get rid of all the wire and rebar once you get him to the table.
If I didn't say it before, I'll say it now. You want to start with a designated space at the table for your pig(s), and keep that space empty. You do not want to improvise during the party.
When you do wire and rebar -- don't do a half-a$$ed a job. Yes, it will fall apart, and yes you will look like a fool. Try and remember that your dearest friends will be helping you turn and move the pig, and that they are complete morons who mean well, have never done this before, and are champions at unintentional physical comedy.