So, decision has been made by me, for me. Upper structure now fatally weakened by me drilling big holes in it...so hack it all off!
I obtained some 8mm clear acrylic sheet, some already laminated fibreglass sheet, with a gelcoated top surface, also about 8mm thick, neoprene foam sheet for a hatch seal, and about 50 off M4 stainless bolts. Proceeded to assemble a new top hatch off of the model. Then got the Permagrit cutting disc out and hacked the top out of the lovely, expensive, Engel kit, to within 25mm of the top edge of the upper part of the WTC. Using Fibreglass Repair Paste, I then secured the new upper deck to the roughened surface of the original kit. filling and fairing in with filler to complete the job.
Imagine green fibreglass paste, sticky tape everywhere, dust, and bricks and batteries to hold the whole lot down while glueing.....because I left the camera at home that night! So no photos.