I have two technical queries for which I'm requesting input/advice. Background: Replacing head gaskets 2006 Pontiac Torrent 3.4l approximately 163000 miles on odo. BUT that is not original engine so actual engine mileage unknown. Heads removed due to several overheating episodes, took to machine shop for cleaning/resurfacing and visual inspection.
First question:
should I replace the valve stem seals as precaution before reinstalling? Have new seals (included in HG kit) but don't want to go falling down a rabbit hole here. I've never replaced valve stem seals myself (usually have that done at shop) so have no idea if I should just leave well enough alone a la "If it ain't broke don't fix it" OR dig a little deeper because I'm already so far in "Whaddya mean you didn't replace the water pump when you did the timing kit?! Now you're gonna have to do all that work all over again, idiot.......'(Yes I know that particular situation won't apply to this engine. But you get the idea, right?) If advice is to replace them now before head reinstall some detailed procedure notes would be really helpful. Please and thanks!
Second question:
Would it be wise to put each cylinder at TDC to install the pushrods? My first time dealing with pushrods and I am terrified of stripping/pulling the threads on the rocker arm pedestals- read/heard too many horror stories and absolutely want to avoid that kind of complication, thanks. Somehow I've got it in my head that I can reduce the chance of stripping or pulling the bolt threads if I'm not fighting valve spring tension during pushrod reinstall. So, if cylinder is at TDC, both valves are closed with no spring tension applying, should be easier to drop pushrod in and then secure rocker arm. Right? Or have I got this completely ***-backward with wishful thinking? I truly would appreciate some guidance here! Again, please and thank you!

Have them do the valves and seals. Install pushrods and torque the rockers. Think. If tightening the rockers were to pull them out of the threads then what happens with the engine running.

Already got the heads back from shop- that ship has sailed. (Shop owner did them as a special favor to me - right now he'* not accepting any new work.because he'* backlogged 8 months )....now I'm having second thoughts so seeking input. You ask "What happens when the engine is running?" Far too frequently for my comfort, the threads pull out while in operation. But the failure is just as, if not even more, ;likely to happen during engine re-assembly. (And I have a theory about that but I need to stay on-topic). This is a pretty well-known weakness of this engine design.. But we digress. I do thank you for your response.
My question(*) remain unresolved. Would anyone else care to chime in? I ask again because I lack experience so do not have adequate frame of reference on which to base a decision. Thank you.

You are far to afraid to be a mechanic. You would bend the rods before pulling the threads.
The only way that would happen is it the lifters didn't compress.
I'm outta here.

I agree with carfixer007 ^^^^^^^ , you should be able to install them any time.

You could turn the engine so each respective cam lobe is *not* pushing up the respective lifter while you're installing each respective rocker. It'* not necessary, but it would solve what you're talking about.

If the threads are in such bad shape that they'd pull out while reassembling, having a pushrod applying pressure a few thousand times a minute would pull them out as well.

Regardless, be sure to torque them properly and to the right spec.