300/440/550 old 440 550 jug question

thisis a question for my bro ... I gave my brother a 550 top end I had from a few skis back .. to bolt onto the 440 bottom end .. but he says the pistons wont fit into the bottom skirt ?? i didnt go over and see him yet.. he just called .. i know its an oldie ( i gave it to his son a year or so back from a combo jetski deal.... it has the old full circle crank and old coupler that bolts on .. so I also gave him th old 550 bottom end too (bad crank on that one) .. he says he used the bottom case from the 440 and the top case fromthe 550 and says he used high strength silicone gasket ******** to join the cases .. i told him .. no u need to use the 3 bond ******** ... what do you think .. will it be ok or should he take it apart and use the halfs together like he did with 3 bond like i told him ? he says he needed the bottom of the 440 case for two bolt holes ? i need to go see wtf he is talking about .. i dont know jack about the 440 and 550s realy .. .. so what do you guys know , any input even with this vague description ??
 
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