Nothing Bakelite comes to mind in the timing of a 20R. It should be double row chain, metal backed guides with a bonded rubber surface. Maybe the running surfaces on them originally were Bakelite, though, can't say. The ones I've seen the past 25 years have been rubber on metal. Maybe the tensioner foot? It has been a rubber on every one I've seen. But I have not seen original 40+ year old 20R internals first hand. Thing is if you lost guide or tensioner you'd know it. It would rattle and maybe even skip teeth, which throws the cam timing off and it runs poorly. So if it was quiet and running well I doubt the parts are timing.
On 22R the timing I think was expected to last as long as a headgasket (about 100k to 150k) but I'm not sure the 20R parts, maybe a couple of headgaskets or the life of the engine.
The problem here is availability. People would upgrade 22Rs to double rows using 20R parts and a deeper timing cover. So that strained the parts for 20R people who actually needed them. The OSK kit you want is T005K. There's some out there still (search also W0133-1899011 or look for 1984 or older 22R in Pickup or Celica). This kit plus a water pump and water pump gasket (Aisin WPT-017) gets you the front end. You probably don't need a new oil pump and the OSK kit should come with a new front main seal. You *may* need to sleeve the crank if your front main seals has worn a deep groove and leaks.
If you cannot find OSK or Toyota boxed OSK (the OEM) then you're in a delicate situation. I would not personally use anything other than OSK but using 1985+ 22R parts would require several misc parts and even then I'm not sure if it would fit with the pan and head. If an all OSK kit isn't found I'd really work hard to find an OSK tensioner at least.
Your choice is to drop the pan, pull the head (this is the Toyota FSM way) or neither (bending lip of pan to fit, least preferred option). Since the 20R has a positive relief sealing surface pan you can get a gasket to put it back on. It's the easiest way to do it unless you want to do a HG. Plus it sounds like you already dropped it.
You may need a couple of woodruff keys. Those sit in slots on the crank to drive the oil pump, Toyota 95161-10519. Those are $4 each peace of mind.
I'll add that those metal backed guide can break. I had a single row kit that used shaved down double row in the 22R-E in my old 1991. The driver side snapped off at the top and got speared by the crank gear. It was a mess. I'm firmly in the "Do it the way Toyota intended" on timing now. Down to using OEM bolts, no substitutions. Oh, also torque the timing chain tensioner (the piston dealie) bolts exactly. I think it's 12 ft-lb.
This is stock parts on a 22R-E, but it's vaguely similar on a 20R. This is before I put the head back on and hadn't yet zip tied the chain up to hold it in place.
