Quoted:
The upper needs to be sear-cut if you'll be using GI auto sears instead of drop-ins.
You'll need a full auto carrier, and complete full auto FCG.
You realize you need to hog out the lower to fit the auto sear, not just drill the sear hole, right?
+1.
There is no commercially sold AR15 lower that can accommodate a full-auto fire-control group without milling the interior. The conversion is way beyond just drilling a hole for the autosear pin.
So as far as which host lower receiver is best ... since you are completely redoing the inside dimensionally, the only issue is exterior cosmetics.
In addition, I'm wondering why an 07/02 would make their main focus the MP5, which is an out-of-production legacy SMG with no potential LE sales. LE looks to newer-generation SMGs today; you might as well focus on STEn gun production.
You are paying your ITAR fee, right?
Please, enlighten me ....