The biggest issue is the plate capacity and being able to somehow put accurate numbers to their capacities. I assume you've gone the route of trying to track down the original supplier and see if they have any information?

Often is may be easier to analyze the truss for the existing load, and then new, and then check each place where the loads have increased. You may end up needing to plywood the joints to feel confident in the load spread.

Depending on the weight of the mechanical, you may just be able to install some stiff strongbacks to spread the load across multiple trusses.

Yes. We tried to find the supplier but no luck.
I thought it might be something something similar to SJI tables. I guess not.
Does the TPI have tables for the plates?

I believe there is a way to evaluate the plates, member PhamEng (if my memory serves me correctly) has previously posted something regarding this. I'll see if I can track down the reference.

Found it, he posted a link to the TPI 2014 document in this thread.

thread507-487754: Wood Floor Truss Plates - Failing

I haven't looked at it, so I can't comment whether it's actually what you're after.

I've gone the route of reading the TPI and evaluating plates before. I remember needing an ESR like this one:
Link

If you can post some more specif info about the trusses I'll try to help.

If you don't want to post the info here you can email me: rsitruss atyahoo dot com