Any of the S&W K, L or N frame revolvers are built tough enough for +P loads, the question is whether you need them. Some of the older J-frame revolvers do not hold up to +P loads, especially the lightweight frames.
Please remember that when you go to +P (higher pressures) you have to give something up so the pressures stay within pressure tolerances for the revolver. Usually you give up bullet weight, which is why you find most +P loads for the 38 Spl with lighter bullet weights so you need to ask yourself what you want to use the +P loads for.
If you reload you can easily roll you own that outperform most +P loads on the market today so again, you need to ask what you want or need the +P loads for.
Given that, your Model 64 may or may not be a great choice for a cylinder full of +Ps. If it is a newer revolver and rated for +Ps from the factory you can shoot them all you want. If it isn't, you can load or should be able to purchase non-+P loads that should do very well for you. JMHO. Mikey.