mmmmmsteak, the sp1 would have needed a 3 prong flash suppresor and a non trap door butt stock. that would make it the first type m16. no gaurds around the mag release, no forward assist. m16a1- forward assist, trap door butt stock (shorter and a wee bit differant then the a2 butt stock), bird cage flash suppresor (remember, only a2's have parcial seration and solid bottom, a1's are serrated all around), gaurds around mag release.. norinco cq311 after hardwear change would be a m16a1 clone and your cheapest route. also remember in vietnam 30 round mags were not the norm, straight bodied 20 round mags were. hope this helps, i'm trying the same. starting with a cq311, have all the hard wear coming, just waiting to recieve and put all of it togeather.
btw- contact, why put up the ####. lol
forgot also vietnam rifles were 1:12 55 grain. nato round and twist rate didn't appear until much later.