You want to remove only the rear bolt, since you need to be able to move the shifter to all positions and then let the engine idle to check the fluid level:
Take the linkage rear bolt off. Remove fill plug. Add WS fluid. Put back fill plug finger tight with rubber O-ring in place. Reconnect linkage bolt. Start engine. Move shifter through all positions. Let engine idle. Remove overflow drain. If you need to add fluid (likely), then repeat all steps, starting with the engine off, until you get a trickle from the overflow drain with WS temps between 97-114F. Tighten up everything at the end.
I think the dipstick assembly was part of the trans casing, not the pan. The parts that can be retrofitted are not easily available anymore, I think.
And if anyone thinks the linkage in the way of access is a bad idea, try not think about the hot exhaust pipe nearby, ready to flake off hot rust chips onto your head (and elsewhere), or just plain burn body parts. It is almost as if Toyota wants you to take it to the dealer.
PS: If you ever remove the pan, make sure you have a wobble extension for the back four bolts to be able to clear the cross-member. Keeping the new gasket in place while you get the pan back up is fun. I wonder why Toyota did not put in a locating pin or two to keep the gasket in place.
As I said before, it is almost as if Toyota wants you to take it to the dealer.
I was in 2-325 the majority of my career
