Yes, there have been reports of a better exhaust. If i remember correctly standard BT 50 with stock cylinder and bore, went 95km/h with custom exhaust... there was a topic somewhere in this forum...
PS: On the picture above is stock bt 50 exhaust, which isn't very bad exhaust, actualy is quite OK, but the silencer pipe has to have 15mm inside diameter to be efective enough. Stock silencer is of a different type, and that is why it has 13mm
EDIT: found it!
viewtopic.php?f=14&t=2432&p=35273#p35273
And about a35 cylinder, this is possible without messing with carters, you just have to modify and extend transfer port outer windows to fit the carters. Some tuners here did it, but the port timings were mostly changed too, and i think most messed with them too much (too high timings), and then the motor wasn't useful enough...
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