i believe you havent any choice unless you want to change all the engine beds etc. the usual is an inverted rubber metal mount which sits inside the wooden engine bed. they are not cheap but readily available from thoneycroft in prreston. they will also send you fitting details from the original thorny book. what are the symptoms that make you think they want replacing as its not an easy job
My understanding is that the Thornycroft block is based on a Mitsubishi engine which is also the foundation for one of the Vetus engines. When I needed replacement mountings for a Mitsubishi I went to the Vetus catalogue and found an excellent calculation page which helped me select the right mountings. I have also had good service on engine mounts from a firm called R&D who also make drive couplings etc and on other parts for my Mitsubishi from a company called Diamond Diesels. Hope this helps
They are the inverted rubber type if it is the T90(Marinised BMC 1500 diesel). I've just replaced the T90 in my Moody 33. They were supposed to have been replaced by the previous owner, but when I tried to remove them the central bolt rotated in the rubber bush and the two side coach bolts were impossible to undo so I ended up cutting the coach bolt heads off with an angle grinder. Then I had to lift the whole engine out in one lump.
The rubbers were knackered, either disintegrating, swollen with diesel or the bonding had failed. Impossible to remove the remains of the coach bolts - actually bolts screwed into a steel cross bar in the engine bed, rusted solid - so ground off the studs flush and glassed over.
Good luck - but do contact Thornycroft for advise, they are very helpful.
If the mounts you are replacing are the 'cotton reel' type mounts, then ASAP supplies do them. Do phoe Thorneycroft though regardless, as they are very helpful when i used to have a BMC engine