Checking the web for info on U47, specifically to modify to U96 I found a shop in Germany selling two nice conning towers to modify the original VIIB type to a VIIC and VIIC/4 version. The kits are designed for the Robbe U-47. I'm planning on ordering the VIIC type and will write a review after building. Look in 'Produkte' and use 'weiter' (more) in http://www.dream-arts.de/
sorry it took some time before answering. Couldn't figure out where you live, but since this is Holland, ordering from Germany is pretty simple.... Dream-arts states under Allgemeine Geschaeftsbedingungen & lieferungen (General delivery and sales manifest) on http://www.dream-arts.de/seiten/agb.html you may order using the 'bestellen/order' form ( http://www.dream-arts.de/seiten/bestellung.html ), paying in advance or on delivery to the postman. Within 24hrs after ordering you will receive a e-mail confirming your order. Maybe just email these guys (in English). Change is 95% they will answer and can give specific details. If not come back to me and I might be able to help.