If he is too fine he will probably not get anywhere to be honest....well in classes down here. If he is a chunkier TB and has a decent neck on him and pulls off a good show then he may get placed, but the true hunters of more ID/TB that also do a good show probably get placed higher
But also depends if the judge is judging perfomance over type or visa versa!!
Have a look in H&H this week - superb lightweight hunter was an ex racehorse! Just because a horse is tb it may not necessarily lack bone/substance or ability. However they do seem to have good memories and those which have raced can take a bit of time to settle at non racing parties!!
Glad you like the one in H&H - that's one of ours! He has masses of substance now, but it has taken 2 years to get him looking right. Other TBs we have are riding horses. It really depends on his type and height.
There are some photos of him in the pictures forum. "some more pics of my lovely boy" I was thinking more a hunter in hand class to start with. I suppose it is experience for him as we do not expect to be placed he has too many lumps and bumps