OK - I attended the new San Antonio Guns Show last weekend and was able to buy some more gear for this new rifle.
Using a DPMS parts kit the 'build' went OK, kinda. The mag latch was a BITCH to fit

requiring much filing on it's upper and lower surface before it came close to fitting in it's 'ole and those trigger guard roll pins don't exactly slide in do they?! - everything else was easy enough and I somehow ended up with a really good trigger pull

.
I also purchased a DPMS quad rail upper complete with BUIS's and the LW contour barrel that I wanted, everything has now been suitably torn apart and stirred and mixed with the components of my existing HB (.750 DelTon ) and I have the LW 'truck gun' I wanted:

and an almost complete lower

just requiring a'target/tactical' style stock (recommendations?)
MP