There's a tab up the top with a database of cars, while it's not complete but there's a load of information there. If you can find the wheel rim size then you should be able to find a corresponding tyre here:
60s all weather tyres
These are raced in FIA historic series so I assume they're period correct size-wise.
Rear tyres were 26" diameter x 18" wide from the early/mid 70s through to 1993. Front tyres were typically 20" diameter x 10" wide by the end of the 70's but from 1981 increased to 25" diameter which remained the same until 1998. In the 60s some teams were using 15" diameter wheel rims but pretty consistently teams used 13".
There was a lot of experimentation with tyres in F1 throughout the 70s (not always scientifically based, e.g. 6-wheelers), I think mainly to do with the cross-ply tyres they used until the early 80s(?) so with a smaller side-wall you get less slip angle so you get more positive turn-in!?