Hi so I have a S4 Rx7 FC from Italy, only the block that needs a rebuild but everything is discontinued, I have a suspicion its also already got some S5 parts on it from another rebuild.
The original plan swap the S4 centre iron and rotor housings to S5, only problem, the S5 front rotor housing is now discontinued.
So my options:
Run NA S5 Rear rotor housings for both front and rear,
Run S4 turbo front and rear rotor housing and plug each coolant hole.
Run S5 Turbo Front and Rear rotor Housing and plug each coolant hole with 9930-62-000 freeze plugs.
The engine originally had a thermal reactor that was broken so will need a custom exhaust manifold regardless.
I have attached some of the images of the block.
Finding part for this has been a nightmare so any help with suggestions is greatly appreciated.

 

welcome to the board.

unless the European spec S4 engines came with a different EGR setup, your intermediate housing already looks like it's S5.

for your rotor housings, any of your choices are viable, but i would probably go with S5 Turbo set because ... why not?

 

According to Atkins Rotary in Eatonville, WA. both front and rear rotor housings are available for S5 turbo and S5 N/A engines. The S4 rear rotor housing, however, is discontinued. Either way, all these available rotor housings are very expensive, ($1,200), with the S5 N/A rear rotor housing being the cheapest at $900.00. When I ordered my rotor housings from Atkins back in 2012, they recommended that I purchase two S5 turbo rear rotor housings for my engine build, since emissions was not an issue in my intended application, (rotary engine swap into a 1975 Porsche 914), and they were only $520 each. Another bonus was that the turbo rotor housings featured the open exhaust port sleeve, (without the baffle incorporated), for a slight power gain. So, if emissions is not an issue for you, then definitely go with the turbo rotor housings. If I were looking to buy again, I would inquire to find out if I could use two of the S5 N/A rear rotor housings in an engine build, given that they are only $900.00 each, then see if I could get the N/A exhaust sleeves swapped out for the turbo version to get the additional power benefit.

Since then, I decided not to undergo the engine swap, an instead I purchased a 1990 RX-7 convertible after I moved to Maine in 2016. I am still collecting engine parts to eventually assemble an all-new rotary engine for my car. As parts continue to get more expensive, I find myself in a hurry to acquire the more expensive parts sooner. I am grateful that you mentioned that freeze plugs, (9930-62-000) are needed for the turbo rotor housings; I totally forgot about that!