LS1 Nova hit the nail on the head. If you aren't going to open it up enough to do a cam or something, I would replace the oil pan and go on with the swap. A h3/GM muscle car pan are good options, holley 302-1 is another popular choice, as well as a 98-01 F body pan. You can find the f body pans with pick up and windage tray for like 150 bucks if you look in the right places. Also, need to source a dip stick and tube for the application the pan is for, GM made many many variations. Here is a good source of pan info
https://www.improvedracing.com/gm-ls-oil-pan-dimensions
My sierra had 197k on it when I pulled the heads to swap a cam and the cylinders looks great. So I wouldn't be scared of anything on your list. Both the front and rear crank seals can be replaced easily enough on the engine, as long as you don't remove the cover, if you remove the timing or rear cover you should pick up a set of alignment tools, they're cheap and easy enough to find or rent *note install the seal AFTER aligning the cover*. I'd reuse the valve cover gaskets if you're pulling them to inspect, I have many times and they are fine. I reused water pump gaskets before and they seal up good, no reason to pull that unless you're going to pull the timing cover and r&r the oil pump, which I don't think is 100% needed. If you go that far you need a new balancer bolt, and they get torqued to like 70ftlb's then another 270*
Look at the rear most bolts on the exhaust manifolds, they always break. Pull all the bolts, others might break too. Any that do that aren't flush should back out with vise grips. Any broken off flush, weld a nut to them and pull them out, easy peasy. Dorman makes a manifold bolt kit, works great, get the metal GM style manifold gaskets, the fiber ones suck.
I'd do plugs and wires if they look OE, check the exhaust manifolds and R&R with new metal gaskets and bolts, remove the little plastic/foam cover on the back of the intake the makes it a pain in the ass to r&r the oil sender, and watch the OPS when you swing the motor in!!