Thanks for all the responses 

I have contacted Ixis to see if he has an original lockdown bar first if not I will buy an original and modify to suit. I have looked at bars on PSPA but although difficult to see from the photo it appears the centre of the NBA lockbar may be pear shaped?

RobM, when you modified your bar, are you using the original 5 membrane switch under the firing button. Just wanted to make sure that if a button fitted to the centre hole, it will line up the original switch membrane, before I drill a hole in a brand new lockdown bar.

regards Derek