yes it will bolt into the S13 chassis using stock mounts. And no, you dont need to convert to RHD. Putting it into an 89-90 though require a little bit more work due to the 89-90 having a SOHC motor and going to a DOHC motor. The powersteering lines from the SOHC will not work on the SR. you can either use SR lines or lines from the DOHC KA, which came in 91+ 240's. Also if you want to use A/C then you will need to either get the SR a/c or the DOHC KA a/c. IIRC there are 4 bolts and the one from the DOHC KA will bolt up using 3 bolts, but it will still hold on fine. The tach that you have will not work with the SR. The SR cant drive the single cam tach. you will need to upgrade to a DOHC KA tach or use an SR tach. I think those are the only main problems when putting it into an 89-90, but I may be forgetting something.
Here's a basic rundown of stuff you will need...

S13 red-top SR20DET engine, complete, used $1850.00
Engine delivery $ 190.00
S13 Greddy Intercooler Kit $1050.00
Heavy Throttle S13 Hot IC pipe for Greddy IC kit $ 90.00
S13 Greddy 3” Downpipe $ 175.00
ACT Street clutch disk, pressure plate $ 325.00
Blow Off Valve (Greddy, Blitz, etc) $ 200.00
Walbro in tank fuel pump, hi flow $ 120.00
Misc Hoses, Fluids, etc $ 100.00
3" Test Pipe $ 60.00
3" Apexi N1 catback $ 450.00
Battery Relocation Kit $ 60.00
Boost Gauge/Air Fuel gauge $ 175.00
14" Electric Fan 3000cfm $ 150.00
Filter/adaptor $50.00

TOTAL: $5045 give or take $100. The IC kit can be had for about $795 but the motors have gone up in prices a little.

That is just an estimate on the price. The price will vary with the brand and where you order your parts from. That should all get you up and running at stock boost. If you have a boost controller, you can up the boost a little bit but I wouldn't go past 11-12 psi on stock internals. You can run 14-15 psi with the stock T25, but after that it is past it's efficiency range and you will not be making any more power.

Somebody like greaser could probably give you a more detailed explanation of what needs to be done.

Hope this helped a little bit