See my prototype electronic board w/connectors. Is it acceptable as a commercial product by Western standards?
The size of the box is limited by the connectors so it is a reasonable enclosure and layout for a splitter type box. Without more information about the circuit it would be hard to say anything else.
The spacing of TTL's is fine (if it works), if this is manufactured in quantity it is unlikely your client will spend the extra $.03 a unit for DIP sockets so the spacing between chips will actually improve. On the other hand TTL logic has been available in SMD sizes for decades and all that extra board space is a huge cost for a product like this manufactured in quantity so it entirely depends on what your client intends to do with the device with regards to the suitability of the circuit design. .
In terms of acceptability as a prototype see below for comments by category
Enclosure
In terms of a delivered product, it depends on what you are expected to present. For something with so few components I would spend more time making cleaner holes for the connectors to improve presentability of the enclosure. You may also want to consult your client about the type of cables being used. They may have hooded DB-15 connectors that would have trouble fitting in that opening, they may also have shielding/grounding requirements for case continuity between DB-15 sides. Additionally PCB mounted connectors that are roughly handled tend to break solder joints so physical screws may be necessary. This looks like an electrically simple device, the professionalism of your design is largely based on a clean look (good mechanical engineering) and a reliable (i.e. bombproof) assembly.
PCB
If this is a one off for a private client it is probably OK to leave on a protoboard (but check with them). If this is a something for a corporate client  that needs 5+ copies or a bid for a bulk manufactured design the client will expect a PCB. I would have a PCB layout ready to replace the protoboard at the very least and ideally already fabricated. Generally speaking US companies and consumers will expect even small electrical jigs like this to be manufactured on PCB's.
Two layer pcb's in reasonable dimensions can be made quickly and shipped internationally, there are any number of PCB houses that can do this for you. Some will even provide you simple layout software with integrated cost calculators that is more than adequate for this application.
Overall
At the end of the day all of this depends on what the expectation of the client is at this stage. If this is a final prototype for a purchasing decision it is probably inadequate from a professional point of view, as an intermediate stage in development with a more relaxed professional relationship it may be fine. This is a prototype yes, but it does not demonstrate that you are ready to produce a final product tomorrow. In the US or otherwise I would expect any serious client to expect a final prototype for inspection to be close to or exactly the same as the delivered product (minus last input by client).