DAF 45 130 Clutch Problem?

Hi can anybody help with some advise on removing a clutch on an M-reg Daf 45 130. The vehicle is a conversion from a post office van to a horse box. The worry is that during the conversion a luton has been added above the cab and the cab has been welded down. There is an access panel above the engine to get in.
Is it possible to remove the gearbox only to sort the clutch out or is it an engine and gearbox out and a bench repair. Also can it be done from below due to restriction with the cab welded down. any advice would be appreciated.