Off hand I don’t recall any requirement for recompilation or re-encapsulation when moving from V5R1 through V5R4 (though V6R1 is a different story) so I don’t think the lack of source code and/or observability is a problem.
As TGTRLS support only goes back two releases I believe you do have a problem if you need to send them actual objects (as opposed to flat files, source code for recompilation on their system, etc). I only have a V5R4 system myself, but I have an agreement with another company (at V5R2) that I can do compiles, testing, etc on their system remotely. In that way I can support the distribution of objects to back level releases. Any chance you can do something similiar?
Another way is Hardware does not permit your client to go to V5R4 have them go to V5R3. Also if you have the source you can save the source to PC and then ftp to Client and recompile…..Rick