I've heard of people putting a bunch of duck tape in there, then filling it with wax to avoid splitting the cases for port matching... It seems like it would be pretty easy not to get shavings in there... Plus it's not like you couldn't flush it out with gas and compressed air... However if you have it off the bike, you are way better off rebuilding before putting a huge kit on there to blow all of your shitty seals out and the high rpms will surely kill some 40 year old bearings...