http://www.az240sx.org/tech/Pinout/
^compare the pinouts for the S13 KAE and KADE ECUS. Due to minor differences it would not be possible to drop a DOHC ecu in a SOHC harness and have it work. furthermore I dont think rewiring the DOHC harness to work on a SOHC motor would net any more positive results (without considering the cost/time spent)
with that said there are other options for tuning the SOHC. the SOHC ECU uses an EPROM memory chip which can be reprogrammed ALOT easier than the DOHC ecu which requires an additional daugherboard be soldered in. If you do a search on NICO or on The BIkirom Forums you should be able to find more information about how this is done and what hardware is required. for your intentions I would reccomend this route. The only downside is getting a clean .bin file of the ECU that you can tune and burn to the EPROM.
another alternative would be a standalone such as an EMS or the Greddy Emanage ultimate thing that's coming out. The EMS works on the SOHC engine and I'm under the impression the Greddy unit will too. that is the more expensive route but would be more user friendly and I would think more flexible (I think the EMS has option to use a MAP sensor)
anyhow that's just my 2 cents.