B16 gearbox housings - don't swap the halves? (YSK-1 bottom half and YSK-2 top half)

[Dodgy Haro]

Hi ppl

I am probably finding this out the hard way now but I believe I read somewhere earlier today that whilst B series gearboxes generally hook up with B series motors, you should not swap the gearbox casing halves between them.

Due to a gearbox casing with broken engine mount points, I had obtained a replacement gearbox top half believing they were similar however when attempting to fit it in place of the original, I noticed it refused to mate. Upon further checking, the original gearbox top half casing had YSK-1 stamped on it but the replacement half I got had YSK-2 on it.

Just wondering if ppl with knowledge know whether they are compatible or not ... given they are made of aluminum, I didn't want to tighten the bolts further to force a fit if there was something in the way preventing this from happening.

Welcome any thoughts. I may just source a complete gearbox at this rate but I seem to have a lot of difficulty sourcing them from local wreckers.