Ok, just try to get your model in SP as close as possible to same as your kite is. Then you will have as precise bridle as possible.
It is ok to be flat, it should be flat. I wouldn't doubt accuracy that much, it may be the best information of kite shape you will have.
Comparing is ok. You decide by yourself how projected shape will be, within those limits PG parts allow. Just try to make it look good, wing will take that shape without much problems (as far as you are not doing anything too extreme).
Of course you use original lines, but they are only raw material to new lines. Don't try to match your design to original lines, it makes no sense because your new wing is different and it is almost impossible task. You must make every line new line, your SP model is done exactly for that purpose, to give new bridle line lengths.
By accident it is possible that some of your old lines will match new lines, but most of them (90-95% (?)) you must cut and make a loop in them according to your plan. Recycling old lines is easier than to use bulk line because ends have loops already, only one end have to be made. Simplest way to make new loops is by knots.
In your design first and second level are much too long, third level is too short. Length from the canopy to the end of the bridle is not long at all, more like short. Towpoint separation is ok.
Your canopy curve is too much in the center, adjust it towards the tips (like 50% or more). Amount of curve is ok.