I started out with a simple "Dropped Valve, replace with JY engine" project that became a Mark Motor swap, and 2 years into that I bought a PI engine and swapped it.
That turned into the swap from hell; the labor alone I have in it is astounding.
I've pulled the engine 3 times for various BS reasons, and have had to buy more stuff each time, lol.
The last time was the tranny dipstick tube, lol.
Don't do that; Do it right instead.
Doing it right means crossing all the T's, dotting the I's, and making sure you aren't shortcutting something; if you do, it will bite you where it hurts most, the wallet.
I'd buy new pistons, do all the bearings, buy a new cam, new lifters, new pushrods; buy the good headgaskets, after making sure the block and heads meet the flatness spec.
I'd Measure the cylinders with a bore gauge and depending on how it looks either hone or bore the cylinders, which is pretty much everything.
It's cheap compared to it sitting, waiting for me to have time and feel like fucking with it again after it breaks.
That's what I'm doing with the mark motor I bought.
I'm now at C-heads, from B-heads and rebuilding IMRCs, lol.
If you want to reuse parts, wait until you're done with the New Motor, and build the other block you have with the reused parts, so you have a spare, should something go wrong.
I have an iron block sitting here that the OG mark parts will go into someday, if I ever feel like dinking with it, lol.
Good luck with the build!