i was in the same situation as you, 176000 miles and even though the engine was still running fine i wanted a bit more power, i decided in the end as i have a run about car i would vr6 the mk2 as i wanted the noise and a bit more power.
i started the vr6 around a month ago and shes coming along planning on 5 months now for completed product as not getting the time.
i'd say if you’ve got the time go for a transplant i didnt think about time, only working 1 day a week on it will take longer than i thought.
at the stage of pulling the engine loom out now LOL
abf would be a good one to go for as well