Land Rover Repair: mechanical issues

Question
just had heads done up on 1987 disco, done 1400 klm and it put push rods through the block, on start up, what would cause this to happen.

Answer
The engine may have been in need of a full rebuild, but you just did heads.  The additional stress may have been too much.  Or there could be an assembly problem after the first job.  Or it could be simple bad luck, or running out of oil.  All are possible