I say a clean LT1 F-body
For about $8-9k you could have a 94-97 LT1 with probably less than 50k miles. And you will eat that MR2 alive
LS1 would be nice but the car will be more expensive and the insurance will kill him.
By the way,
My LT1 put down 280 HP and 305 lb-ft at the wheels...only real power mods are a K&N and an exhaust cutout
Most LS1's put down around 290 HP and 300 lb-ft to the wheels stock. 305HP/320lb-ft has happened but thats not the norm at all, regardless of what everyone says (I spend WAAAY too much time on F-body forums lol).
And the Optispark isnt that bad...if youre not afraid of it.....they are like $150 from Autozone right now, and you and a Haynes manual could replace one in an afternoon if you had to.