I've done it twice on my own rigs and helped a couple of people do theirs.
I might be a minority opinion, but I think the H55f is a great upgrade if you wheel or do a lot of off-road driving or even paved highway. I opted not to do the H55 for an 87 I had and it was mostly an around-town truck (Los Angeles, that is, where it seems like there's a stop sign or stop light every 50ft) and the 4spd was way easier on the legs and far less shifting than the 5 spd in my '85. I was very glad I listened to a local LC guru and kept that truck 4 spd. Toyota knew what they were doing for an 'Estate Wagon' which is what the purpose was in the States, at the time.
The H55f driving consideration aside, is a very robust, heavy-duty transmission. If you need a low 1st gear, you'll love it. If your avatar is your normal environment, I'd say you need it.