I don't have a 350, but I do have a 400. It is basically the same thing, externally wise, just a small block. Right now it runs like crap because the carb on it sucks and needs to be messed with, but when it runs good, it runs awesome. A 55 is pretty heavy and I have no problems what so ever moving it around with the 400. I haven't really worked on the 55 much yet, but I want to clean everything up in the engine compartment when I get to it. I want to put some type of fuel injection on it soon, just waiting to finish the 40 first.
Got a rebuilt 350 sbc. Runs like a champ. Quadra-jet needs tunning but I got more power and torque than I know what to do with. Fuel economy sucks but I have a 3 mile commute! I didn't do the conversion but I understand its pretty much just like doing a 40. Check with Advanced Adapters, they will know exactly what is needed to mate up a 350 in a 55. Good luck.
I threw a junkyard 350 and sm420 into the pig a couple years ago. It wasn't too bad of a swap. When it's tuned right, it runs like a champ! Go 350!!!
As far as adaptors go, I bought the 350 engine mounts through Wardens (defunct?) that were actually Advanced Adaptors products- same with the t-case crossmember. The 3/4" adaptor plate between the 420 and the 3spd tcase was warden's, but there are a few others who make them still. The only note I can add, is that the crossmember to hang the t-case in back- it is different for 55's, because there is more room between the frame rails on a fj55, than on a fj40.
If you have an engine hoist, a buddy that can weld, a level, a cutting torch or cut-off grinder, and the necessary adaptors, engines etc... then you're set.
It's just like changing the oil, only you're changing the entire engine instead... hehe.
Oh yeah. When I did it, I was told that I needed to go with power steering- or I would have clearance issues. So I did. I don't know if you can get by with out it.... Just what I was told.
I can't find any pics of the 350 actually in the pig- but Here's the reason why I went 350... I bought the entire pig for $1200, and it was going to cost me more to rebuild this thing, than the 350 conversion. Hope that helps....