if they have a tig welder, it should be very possible, i know its possible to weld cast aluminum... same as welding lifter bores in 5hp briggs. i like the idea of bolting it all together then welding so its straight on there. like toofarnorth said.
also the first time i took my 5hp briggs apart, i used the claws of a hammer to pry it off, i got the engine after it sat outside in rain/weather for 2yrs, and the crankshaft was rusty around the point of the oilseal, making it really hard to get off.
try seeing if yours is rusty there too, i sanded mine with sand paper, not too much tho, just to take the rust off, the put a little oil on it.
Good luck,
BAMBY