I took a look at the serial number on my Grand Prix earlier today and it is 2920000. It, like I'm pretty sure yours is, was made by Gazelle in the Netherlands. The good news is that they used the standard bottom bracket shells. I avoided the threading issue by re-using the cups and bearings on mine, but they should be English threading. If you have a LBS or co-op you like, get them to help you order the parts and they'll have an English-threaded cup for you to try out, like Charles mentioned above.