I looked into doing this conversion on my altezza but decided im going to turbo my beams engine instead.
Be prepared to spend a lot of money on this conversion.
Them r154 gearboxes are nearly making as much as a 1jz now,about £700 up. You should look into a w58 gearbox, a lot cheaper and can take about 400/450 bhp as long as you aren't giving it constant abuse every day
Cos of the wiring you can lose some functions on your dash and the heater might not work right.
A lot will say you can use different mounts from the gs300 or a jzx100 but I would say your best bet is to speak to Phil from vibra technics.he will make you a set that will bolt straight in.you need to make a custom gearbox mount too.
As for the wiring I don't think to many will make you a loom with out the car there for them to work on.
But try Simon from east coast custom in Lisburn. he has done this conversion for people before and has a wealth of knowledge and he could do the custom prop im sure.
0044289266655 is the phone number and just ask to speak to Simon.
As for the remote shifter I don't know, some said I needed one others said I didn't. It depends on how far back the engine sits I think.
Then it's up to you what ecu you want to use.
If you have any other questions drop me a pm lad