I have pretty much all the same parts you do mate.
I started with a TM airsoft Thompson and the G&P kit.
Then I bought the Vents/Triangle/front block/Stock from Phil S. and
a real SPAS cage/grip
Because the counter from the G&P kit only counts down by actually firing BB's out of it I needed to keep the lightgate functional. The problem is that this was originally housed in the front triangle on the G&P kit. However, DATA has since made a system for attaching the Thompson to the Spas cage which also allows for the lightgate to be kept and also now hidden inside the shrouds. He also has detailed drawings of modifying all the PHil S parts and came up with a nice stock locking mechanism similar to Rook's. He has offered to send these drawings to people who want them BTW, should be very useful for you.
You can see some of the work done in this thread here
http://forum.alienslegacy.com/viewtopic.php?t=2321&highlight=data+mod
All of this was done with the G&P shrouds in mind though. I am a big fan of the G&P shrouds, despite the little inaccuracy at the back end as they are pretty damn sturdy and a great flush fit with each other.
So to sum up, I would get the G&P shrouds
Cheers
Darren