bmw m10 confusion!!!

Hi, I have a 2 door E30 316 (M10B18 Carb) with a set of Mikuni/Suzuki GSX 40mm carbs. I am interested in swapping the either the bottom end for a 2002Tii block or the entire motor as I think the heads are similar (I would like to retain the big valve setup).  I hear that  swapping the 318 head onto the Tii block is pointless due to the flow on the Tii head anyway and that I would have to machine the 318 head to work with the Tii block?  If I use the entire Tii motor can I run a D'Bilas 292 10mm lift cam without doing any head work or machining to the pistons? I also want to know the difference between the stock 316/318 header and the Tii one, is there any? How hard is it to get the 318 or the Tii motor to 2100cc, can I use M30 535 pistons with an overbore? It's all so confusing, now I've got a headache again! Now here's another issue..... I would like to convert the car to pillarless (a'la 3.0csi) by using the frameless doors from a convertible and cutting away the 'b' pillar and replacing the rear window with Lexan. Do you think the car might survive if I install front and rear strut braces to compensate for the loss in rigidity? So many plans, so little knowledge!