Mike B has got the right number. The box mine came in also has the same number with a zero in front (03847058) so you might try that if the other doesn't work when you order it.

To dissasemble, remove vacuum hoses, then remove the ten small bolts at the periphery. The outside cover should come off. The diaphragm is between two plates. Put a box wrench on the shaft behind the diagphragm (towards the differential carrier) and one on the outside to remove the plates and diaphragm. Replace the diaphragm with the same orientation as the original and that should do it.

Kent

1937 Chevy 1/2 ton
1942 Chevy 1/2 ton
1947 Diamond T Model 509
1951 Chevy 1/2 ton
1950 Chevy COE Model 5700 ~ "Barney" ~ And more pix