Without going into details :

When going for one mainsail only then have it custom made for 140 + 130 lbs = 270 lbs (122 kg); as stated earlier it should be possible to have this done for no additional cost or at the most a very small amount.

When going for two mainsails then have both mainsails the same size (area) and just have the sailmaker alter the sail cut and luff round. Area is not much of a concern; i.e. it won't help you much at all to get a smaller sail. By far the biggest gains are made by changing cut and luff round.

Don't think you can really use the singlehanded mainsail for heavy wind doublehanded usage in any competitive way. In addition depowering the F16 rig for heavy winds is quite easy and far reaching. Don't worry to much, just learn the tricks and you'll be fine.

The depower tricks themselfs are really easy. Derotate the mast and pull simulatiously the downhaul and mainsheet really tight. And I do mean REALLY tight. This will make the sail really flat and have the top of the mast bend of considerably. The last looks scary but the mast can take ALOT of flexing so down worry about it. These tricks will calm the boat right down.

I should add here that having two mains is a benefit but not really necessary. Having the mainsail cut for your expected doublehanded weight is however strongly adviced. This will make you fastest and will make you competitive again all other F16 crews and go a long way in make singlehanding more manageable. There are no bad sides to that approach.

Wouter