Only replace the rear main and trans seal if they are leaking. Not leaking is the best you can hope for and you already have that. The trans seal would have been done on the rebuild 26K ago. Replacing it may make a leak.

About the head gasket, if it is dry now it probably has been replaced. So no I would not change it.

Are the oil pans the same? Look closely to see if there are any clearance problems.

Do consider new motor mounts, trans mounts, flex disks and center support bearing unless they are excellent. Look at the water pump closely for leaks too and change it if necessary.

Worn steering linkage would be rather accessible to replace while the trans and motor are out.

My 93 300E 3.2 has just over 360K and ran incredibly well but the head gasket is leaking and at 360K I probably will not do it.

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