"relatively easily" is a very loose term...
from a strictly transmission to engine compatibility aspect, any 6G7x motor will bolt up with very minor issues. This includes the 2.5, 3.0, 3.5 and 3.8 motors. Additionally, some Kia/hyundai motors were derived from the 6G7x series and also can be used. Knightmoves 3.5 DOHC
is a Sedona minivan motor and the Hyundai 2.7 is also a 6G7x derived motor.
regarding compatibility with the chassis, only one motor mount needs to really be adapted/changed to fit the other motors (passenger side load bearing mount), but with a motor swap comes additional challenges such as intake and exhaust plumbing, power steering and A/C, and finally, the ECU.
So far, those of us that have gone with different motors, 24v 3.0 SOHC for me, 24v 3.5 SOHC for c2xejk, and 24v 3.5 DOHC
for knightmoves, we all have ended up with a standalone ECU (Megasquirt in all three cases actually).
Ultimately it comes down to a few more questions:
1)what is the role of the car? daily driver, fun project car or all-out race?
2)What budget do you have?
3) Can you afford the downtime and customization needed?
If you are limited time or budget-wise, a newer 12v replacement may be the best way to go. There are bolt on turbo headers available and you can get a 12v turbo running fairly cheaply with reliable power at or above 300whp. Barring such things as acts of God and the like, the 12v motor is quite strong and reliable.