First, can you furnish us with some close-up pics of the "work in progress"?
What kind of SKS? "D" type or the conventional fixed magazine one?
Still got the folding bayonet on it?
Were the carrier, breech block and receiver cover already installed?
I guess the trigger/hammer assembly was separate. When attempting to put it back on, first, make sure the hammer is ARMED and the safety ON.
Then place the magazine assembly's front locating lip in the corresponding recess and pivot it to the back. Now, holding the magazine in place, slide the trigger/hammer assembly in place, locking the magazine's core.
VERY IMPORTANT: PULL THE CARRIER TO THE REAR TO ALLOW THE MAGAZINE FEED LIPS TO BR CLEAR OF THE UNDERSIDE OF THE BOLT! THEY EACH FIT IN A GROOVE ON EACH SIDE OF THE CARRIER. FAILURE TO DO SO WILL MAKE IT IMPOSSIBLE TO SEAT THE MAGAZINE'S CORE PROPERLY.
Then, slap the trigger guard to force it to catch on the latching pin going through the stock and connecting the back of the receiver to the trigger/hammer block.
Sometimes, some fitting is necessary in order to connect these parts between themselves.
Good luck!
IMPORTANT:, when reassembling the upper receiver, remember the WAVY end of the main return spring goes INSIDE the carrier.
PP.
