capt368:
I hope this is the answer or part of at least.
To extend the floor board etc. you have a couple of options.
Measure from inside the body to the outside (if you do not have a contour gauge on the workbench see any hardware store in the woodworking section) you can trace the outline by placing the body over the sheet of styrene. The height of the floor to the door sill and the width between closed door and the seat will have to be gauged by you. Using the template you traced onto your sheet styrene cut out the shape and number necessary to "stack" or laminate together to give you the scale height and slope of the inner floorboard. A little superglue will secure it to the body and then it is just a matter of sanding and shaping to get the correct sit.
Reattaching the door. I will assume that you have built up the door after you cut it out from the body to look like the real thing. It may take a little trial and error to get the correct sit however try this. Take a length of sprue and cut two equal size pieces sand the top and bottom flush. Next, locate a piece of sturdy but thin gauge brass or suitable material wire. (I use the wire from the bottom of keys off scrapped computer keyboard keys the space bar has the longest length) Now using a pair of needle nose pliers form "hinge" pin (Square bottom 'U' is the shape you're after) Cut the centre of the squared bottom in the centre leaving you with two "L" shapes. Drill a hole in your previously cut sprue to match the thickness of the wire used and insert the wire. It is best to place both in the same direction with the longer section of the "L" on top. Cement your sprues inside the body at the height that would match the hinges on the real car. Mark and drill the mating holes on the hinge side of the door. Super glue the L shape to the door and place back in the sprue "hinges" mounted in the body.
I hope this is clear enough. If I have totally confused you I apologize. It is quite straight forward when you actually have "eyes on" the kit. You could also locate a copy of Detailing Scale Autos from Kalmbach, there is an excellent article in it that describes this modification with photos.
Hope this helps.
Cheers;
Gregory