Advice wanted on installing used 258/TF999 combo

Got my tired 258 & T-5 pulled. Have a 258/TF999 as replacement(s). Replacements sold as being 'good to go', having been pulled out of '85 CJ7 getting a 4.3 swapped in.

What should I be replacing/doing to replacements while sitting on dolly/hanging from hoist? (I am NOT separating the two.) No apparent rear main or oil pan seepage, so I am not touching those either. I do intend to check the timing chain/gears.

I am thinking motor mounts, tranny mount, tranny torque bushing (or whatever the tech name for it is), ... What else? Recommendations on going w/ OE rubber or poly mounts?

Is there any kind of seal, etc. in the T/C end of the tranny that ought to be replaced? Anything between TF999 - D300 that is not present between T-5 - D300?

Easier to pull D300 and attach to tranny out of Jeep (then wrestle that long, heavy monster into Jeep or attach tranny/TC in vehicle? (BTW: What's a 258/TF999/D300 weigh altogether? 8-900 lbs?)

Anything else a tyro might miss or forget?

Thanks!