a fella was saying to me that its possible that the conrods or 'little end' could be damaged
but the fact the each pair of piston, on opposite sides of the engine are at equal heights must indicate that the conrods are ok
I'm not an Alfa Mechanic so i need advise how best to proceed.
ONCE will be enough to do this job
Very rare for rods to be damaged on a belt failure - you need some serious hydraulic effect to bend the rods (i.e. sucking water in from a flood), the valves are the weakest point and will always bend.
Small ends won't damage either, they're a very hard nickel / silicon bronze.
In most other manufacturers, the big ends won't even damage (seems to be an Alfa problem, though I have heard some Porsches do the same).
You won't see big end damage by turning the engine over. What happens is as the shell bearing takes an impact, (piston hitting the valves), it causes a small flat spot on the shell. It then runs on the flat's, not the nice round bearing it should, hence in time they wear out the bearing material on the shell, leading to bottom end failure.
V6's are quite strong, but if you want peace of mind, pull the sump off and have a look at the shells. For the sake of anaother £60 or so, replace the lot.
Havind said that, you may get away without...