These pics should make it clear how they go. In the top drawing, the holes to use are the lower holes labeled LS5 and L37 etc. The upper labeled LG4 are Chevy holes. You should not need to do any drilling. Something's wrong if you have to drill.
ENGINE MOUNT HOLES IN THE FRAME by
grand73am, on Flickr
DSCN3257 by
grand73am, on Flickr
DSCN3260 by
grand73am, on Flickr
LEFT by
grand73am, on Flickr
RIGHT by
grand73am, on Flickr