91-96 engines use a 35mm lifter, which are available in a lightweight design sold on the 60V6 store here. 97 went to the smaller diameter lifters so there are no options for them that I am aware of other than aftermarket stock replacements.

4.6 SOHC Ford springs (from a 97 thunderbird) will fit the 3.4 DOHC. They are a little stiffer and coil bind at a higher lift so a cam regrind will be tolerated more easily with them. You will need to use the 4.6 valve guide seals/seats, and pull the seal out. Then grind the seat part so the lip for the stock seal is gone. When you install the stock 3.4 seals to the guide, the 4.6 seat will fit over it easily. Comp Cams 26113 is the spring I used for test fitting. Manley also makes some springs but they are a lot stiffer and I haven't tested those.

Comp steel retainers for the 26113 spring are also recommended, along with the keepers. The retainers weigh 8.4 grams compared to the 13 grams for the stockers. There are also titanium versions available but I haven't bought any to weigh.

No known valves other than custom ferrea valves.