There are plenty of TBV's that come on the elbow, the pic that the OP posted shows the bracket that very neatly mounts to the elbow, also mounts the knock module if equiped with one. Neither the 4.3/2bbl that came with my '04 originally or any of the base 5.0 2bbl engines i've seen have the knock sensor.
Back to the OP's issue- thats why I suggetsed he check the total advance to see where it is coming in at. When he said the mechanic didnt set it in base mode before setting the timing its likely that the timing is retarded 10+ degrees. Its possible that the module is already putting max advance in and why he is seeing it stay at 10 degrees all the time. Its tough to tell as Merc doesnt give a ton of info on charts of the TBV advance curve.
Thats why I think first things first here if he can properly get it into base mode we can see how mauch advance he is clocking in. I think my 5.0 module gets like 26-28 total at like 3 k rpm. Kind of off the point- I have a 5.7 module as a spare that came with a knock system that clocks in a little more even with out the knock system hooked up, the V6 module off my original engine gave like 24 degerees total starting with 8-10 intial. Bottom line he should be doing ok (maybe not perfect) if he can get 24-28 dgerees total.
TB V is the hotest spark Ive worked with on akk my boats and cars, so if he has a module issue Ive bought two modules on ebay for like $150-200 each, (one for my repower, one for a spare).
I think after that he can look at the plugs etc. depending what his carb set up is. If he has a more of a performance set up carb jetting vs edelbrock 1409, it may be rich coupled with a f'ed up ignition advance that it cant get out of its own way currently???
