I would...
1) do whatever I had to do to get the dimensions perfect. That could be as simple as a recoil pad to get the LOP close. Close on the short side is good enough. Close on the long side is an abomination. A Beartooth comb riser kit will make the gun competition ready, if not very pretty. It's a wonderfully serviceable but non-invasive solution should your flirtation end prematurely. It also allows you plenty of latitude to play with comb heights until you know exactly what you want/need. Since you're asking about dimensions, you obviously don't know yet and any but the minimum investment would be foolish.
2) make sure the safety is manual...non-automatic. Or disable it altogether. Open the chokes to the same in both barrels. If you're bound to be forever a "fun shooter", a pair of LM's would be good. If you contemplate competitive clays, a pair of Mods would be better. Some would suggest more open, but LM will allow you the benfit of shooting 7/8 and 1 ounce loads and rarely, if ever, chambering 1& 1/8 ounce. A pair of Mods should negate the use of 1 & 1/8 ounce entirely. I shoot a pair a bit tighter than that and never question them for FITASC, bunker trap and long bird games.....nor non-registered skeet, for that matter.
3) why 2 of the same chokes in a dblgun? First, consider how many superb clays shooters don't feel disadvantaged at all with a single choke in an autoloader. Second, consider that, outside of skeet and trap where all the targets are taken within a fairly narrow range of distance, choke is always a compromise. Seldom do you have the ideal choke for both targets in sporting clays. Having 2 chokes with anything less than 10 difference between the two is just silly. With a difference of 10 or more points, you'll be agonizing over which one to use for which target and sure enough you'll be calling for the targets wondering if one is too open and the other too tight. Better to have 2 that are always enough, without ever thinking about it. Twiddling with choke tubes and barrel selectors is a distraction. Mental focus is a scarce commodity on the clays course; gadgets don't help.
