MAX PSI sidewall ratings should only be used as a "do not exceed" pressure. Tires are designed to be used on multiple vehicles that would all have varied recommended tire pressures. Use your owners manual to determine the correct tire pressure for your car, not the sidewall (just don't exceed the sidewall rating and chances are you won't be close to it anyway). Most modern radials like a few more psi than what your manual would typically call for though. But only a couple of psi.
On your TR3A, the manual calls for 22lbs front and 24 lbs rear. Many owners find that with modern radials something more like 30psi front and rear gives a good compromise between wear, handling, comfort and mileage. If you have been running 42 psi, you have probably been getting good mileage with a rough ride and "loose" handling.
I have never heard of wire wheeled tires needing more psi than steel wheeled tires. If so... news to me (wouldn't be the first, won't be the last I'm sure).
Long post short... the psi rating on the sidewall has nothing to do with what pressure your should be using on your car. Only a pressure you should not exceed.