re TR7 exhaust valves

[huw jones <desrads@domain.elided>]

Fascinated to read Tim Buja's posting about exhaust valves. My motor is 
(still) in bits at the moment (another story) and I find that the valves 
on the right bank are labelled 155524, and those on the left bank are 
labelled 15524 VL. Can anyone explain this and confirm whether or not 
they are  all OK for unleaded? (could it be connected with the left hand 
bank's pistons having been fitted back to front by the last 
("professional" but nameless) reconditioner:-) ) BTW, would you turn 
these pistons round on reassembly or leave them be as they are run in at  
only a few thousand miles since the rebuild. Also any opinions on 
specialists for head skims etc in the north east of england would be much 
appreciated.
Thanks
Huw Jones