If you can find out which is which, there are several earlier version Blasts on German ebay for cheap.. I'm pretty sure at least one of them had the WS7 internals.. Was either the V2, V4, or V5....
V2 Info:
http://www.rmv-lounge.de/2012/01/24/...mited-edition/
Look up "rb blast" in modellbau on ebay.de, and you can find info about the V4 and V5. The V4 is based on the WS9... So not sure how that relates to the WS7...
ps - Just read that the Blast V1 is a WS9 with different head and carb.. Bit harder to find, but they are out there...