I was reading through the Peerless Manual I sent... it seems the brake could be mounted on either side but no mention of splitting cases for brake repair. Like you thought.. you must have some variation of a 915 trans. The diagrams in the Peerless manual appears that
all those similar models 700 thru 900 series all have a typical removable lower brake housing ..
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But your pic ... doesn't seem to represent that !!! ....
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SO ... it's beginning to seem .. like the trans may have to be dropped if you can't get the pins out ... but you may only be able to replace the pins and MAYBE the outer brake pad plate and pad ... PATIENCE ... keep working on the pins ... actually , ..I believe the only important function of these trans brakes is to stop trans moving gears to allow shifting of gears ... pulling the engine throttle back usually slows the tractor itself ... granted the brake is there for helping in that issue . As usual keep us up-dated ..Boobala