I assume that all 800 parts do not move.
Fix any parts that have no motion at all.
Demote parts that belong together in logical sub-assemblies. (I window select, demote and then turn off visibility of constructued sub to make next sub easier to select.)
Fix any parts in those subs that don't have any motion within the sub. Mate those that do.
Make subs that do have parts with DOF Flexible.
Fix any subs that do not have any motion.
Mate remaining top level parts and subs that do have motion.
I doubt there are all that many of the 800 parts that have relative motion.
By the time you fix and demote - I'll bet this would only take about 30 minutes from start to finish.
You sir are a legend...
it never dawned on me that i could do that...
I've done one major component already..
so at this rate... (and I've only got about 6 bits that need to move and look impressive.... I'll be in bed at normal time and wont need to burn any midnight oil)