I have just bought a remote glow filler valve (Dubro Kwik-Fill) and need some advice please. I try to get the tank centre in line with the carb spraybar when fitting as this seems to be the 'ideal' but here's the crunch - does the Kwik-Fill valve also need to be on the same centre line or can I put it more or less where I want to ?

Yes, you should keep the filler at the same level as the carb and tank.

Are you putting this on a cowled engine???

Thanks Viper - yes. Is there a problem I am building in here ?

The springs in that Dubro unit sometimes weakens with use and introduces air leaks to the system. But if you're using a cowled system, there's little you can do to avoid one of these. I'd recommend the Sullivan filler instead. Less moving parts, and avoids the leak issue.
Here

Theoretically it doesn't matter where you place the fuelling valve because the fuel pressure to the engine is determined by the tank position. But there's other considerations such as keeping the fuel lines as short as possible whilst leaving enough slack that you can get the engine cowl off

Having said that, I always mount my valves in the side of the cowl, rather than trying to hide them underneath, because they're easier to access there. That automatically puts them more-or-less at the same height as the carburettor. I also use larger than usual fuel tubing to minimise the pressure loss in the longer lines