Looking for a 5.7 liter to fit a '90 TA GTA

[90tagta]

Right now my '90 TA GTA has the 5.0 with the 5-speed but its not in the best of condition motor wise. It's got almost 200,000 on it and can tell its aged. Every time i look at it it seems I find a new leak or something else wrong. Does anyone have or know of anyone that has a 5.7 with low miles they're wanting to sell. Also to go along with this, has anyone changed engine and what troubles have you ran into while doing it? Thanks, ty