Block stamp identification

[Jrtm]

I've got a new national tower block it's clearly an old new block, I don't believe it's ex mod (most mod stuff for these I've seen are coated red) this has no scratch marks where parts would have been bolted on, there is no even slight water residue, its also coated in extremely old protective grease that has gone hard over all the liner seal edges, every bolt and stud with nuts, all over the cam ways ext

There are no stamp marks at the timing mark it just has 3 number and what looks like a q.c or Lloyd stamp on the top of the tower between 2 water ways.

Numbers are 358

 

Anyone got any ideas are these a national block tower number e.g. number 358? Or are they an mod number? I know of a few block around that have sim but different stamps. As said it's not got a g.u. engine stamp