Help with Subfloor

We have just lifted a house and are about to start building under. The steel posts are in and we need to put an additional 16 posts in for the bearers to attatch to and using the existing steel posts we will get some brackets welded on to attatch the bearers as well. What Im not sure of is the easy way around getting the bearers level. Does the welder come in first and use a dumpy level and put the brackets on in the exact position and then we can attatch the bearers and go from there or do we get the bearers in the exact position then does the welder come out to put the plates on. Hopefully Im explaining it well enough sorry if its come out where Ive confused you all but hopefully you get the general idea. :confused:

save time plus $$$ go though and mark the posiotion for the weilder ready to go all he does is weld.