What kind of plugs go into the speaker ports of this reciever?
Really old Samsung proprietary connectors.  I've seen these before, but many years ago. 
@folkfreak...great job!  I looked and looked for those connectors and didn't find any.  Way to go!
They were kind of standard on everything in the early 70s, my parent's system had them -- also very common on all that nice B&O gear from back then. The DIN connections for the phono and aux inputs are always a give away that these are the connections you need -- and of course many (e.g. Naim) would argue never to move away from the DIN standard
At this point, since the originals are likely unobtainium, test leads...

For the truly driven, opening it up and some substitution would be called for.  The warranty went away long ago...

'Course, the next question is: Why? *L*  Some vintage is worth keeping around, but....*shrug*

I've got an old totally mechanical Rabco TT that actually works and is kinda amusing to play, but I don't subject any vinyl that I like to it.  Not worth anything, but it's a museum piece to a tangential fan.  If this fits your description of such, whatever boats your float...;)