The old style TB(my fav style of TB) were much thicker then the modern day TB. Old styles are heavily favored for sport horses. Irish TB's also tend to be much thicker then North American TB's as well. So there is a good chance he is TB. If he was crossed with anything I would lean towards foundation bred QH or possibly a lighter warmblood.
But lot of the older style TB's are becoming more common these days so there is a good chance he is. I would be interested in knowing his blood lines.
BB ~ 2014 Trakehner Bratty Mare ~ 1993 CSHA Em ~ 2007 Standardbred