Regarding the connection to the h55f trans and clutch they both have a 270mm plate but the input shaft that the clutch rides on is shorter on the 2h h55f version.
You need to change the bell housing also to fit the 1hz to the 2h h55f ,,, so your best off using the hzj 75 with the older trans version before the 1hz and r151f change that was made back in the day.
If you change to the later 1hz and r151f then to fit into the hj 7x chassis you would need to move the location of the gearbox which is a harder job... if you stick to the h55f with the h55f from a hzj75 then at lest you have the gear box mount in the correct location. Of course if you go with the later combo then you have to relocate the gearbox and engine mounts as with 1hz and h55f the gearbox mounts are correct and just need to relocate the engine mounts.
As all the h55f gearboxes are super old and have probable high miles/kms then best to get the box looked over and rebuilt.. Hope the info helps.. Tarah 4 now!