[Safari Larry]

Condolences on the loss of your wife, that would surely be very difficult.

Onward with your dream (hopefully not nightmare) and making some $$$ for Steve B (bought my 60 engine from him). Here are my thoughts and opinions.

As I see it, there are three major issues you must deal with, (1) motor mounts, (2) transmission linkage, and (3) trans mission cooling.

(1) motor mounts: two ways of doing it, (a) use pre 59 mounts, (b) use 59 mounts.

(1a) use front 55 front mount, no problem. For the rear trans mounts, Jack has the right idea: "It's possible a late-'56-'58 bellhousing (with rear engine mount bosses) could be used between his '59 engine and tranny- but I don't know for sure." I'm not sure about that either. Maybe? If you can do that, then you would need 56 CC crossmember or 57 crossmember for rear mounts. You would need to make a couple of small adaptor plates, not difficult.
(1b) weld in mount points on frame for 59 engine side mounts and use rear trans mount with a custom crossmember. I've heard of this being done but with a problem. The engine mounts caused twisting of the frame. So, if you used this approach you would also need a crossmember near the engine mounts to prevent the twisting of frame (I think). This doesn't seem like a good choice.

(2) for trans gear selector linkage you might use a floor shifter or maybe a 56/57 steering column with the P position. Don't know much about that. For throttle linkage, the 55 linkage might work, not sure.

(3) transmission cooler might be done with a 57 auto trans radiator which has trans cooling in lower radiator. That would bolt into the 55. Otherwise, you might install a trans cooler somewhere under the hood towards the front, or perhaps a custom radiator.

These are just my beginning thoughts for further discussion. I likely haven't thought of everything and I'm not an "expert" on doing this!