I just recently unknowingly bought a S4 Manual Transmission. The problem here is that my chassis is a automatic S5 transmission, now I found a bracket to put the manual conversion to the auto chassis. But Im worried if the S4 Manual transmission would work and fit fine into the S5 chassis. Because I originally was under the impression my trans was a S5 manual. And I see that their mounting Y brackets bolt up differently. If I bought a conversion mount for a S4 trans and put it on my S5 chassis. Will everything fit okay? Or would I need to buy a S5 manual transmission to do the conversion???

 

As far as I know it will fit fine, but I'm not sure of what combination of parts you need to make it work. You also didn't say what trans you are putting in the car. N/A or TII as that matters as well. Going by this old thread
s5TII trans with s4TII shifter, clutch, and flywheel - RX7Club.com - Mazda RX7 Forum
Looks like they are doing the opposite of you by putting a S5 trans in a S4 car. Going by Banzia-Racings posts to mount a S4 manual trans in a S5 car you need the Y bracket from the S4 and the S4 crossmember that matches your transmission N/A or TII and all the little rubber bushings that go with it.

 

Mb yeah its a N/A S4 trans into a S5 chassis

 

So I think you need the S4 Y-bracket and S4 N/A crossmember and associated rubber bushings/mounts. Unfortunately, it looks like the bracket is NLA from Mazda but ne N/A crossmember still is.
TRANSMISSION MOUNT REAR, S4 “Y” BRACKET—NLA— - Mazdatrix
TRANSMISSION MOUNT REAR, 86-88 NON TURBO MANUAL (SADDLE) - Mazdatrix
TRANSMISSION MOUNT REAR, 86-92 SIDE OF “Y” - Mazdatrix
or TRANSMISSION MOUNT REAR, 86-92 SIDE OF “Y” COMPETITION - Mazdatrix

 

as far as i recall the automatics had a unique mount point on the frame, the stock stuff for a manual swap won't work even if correct for the year. regardless you will likely need to make an adapter somehow.

the automatic mounts sit further back than all the standard trans mount cars if memory serves.

if you sourced a conversion kit you should check to see what parts it requires, often times it eliminates the saddle altogether. the answer might be better suited for the folks who made the adapter without seeing where it mounts to. the adapter should get you to the correct point on the transmission but i have a feeling the different mounting styles of the transmission are going to bind you up.