Though underpowered, Keeping it in stock condition would be my recommendation, coz there are not many stock ones around at the moment.
QG18DE would be more powerful than SR one. QG15 that I swapped into my B13 is a super fast engine, QG18 is many times more powerful.
You can check my thread about engine swap here: https://www.pakwheels.com/forums/engine-transmission-powertrain/199212-engine-swap-nissan-sunny-1991-b13
and also @star2's thread about engine swap.
But again, a fully stock one is a unique thingy that I would prefer over a swapped one running like a bullet.