If you just do the bolts replace them with the same stuff. You're still supposed to do the big ends but at least you have a slightly better chance of sneaking through.
If you go to better quality fasteners you're in the deep stuff. If you reassemble with out rebuilding the big ends you're asking for trouble. If the engine has been recently freshened then you probasbly don't have to worry or do a lot of ring/cyclinder remanufacturing. If you are looking at 5000 - 10000 or more miles then you will need to hone the bores and replace the rings.
The temptation to cut corners when you do the build is powerful. Remember when you have to pull the engine to re-do what should have been done right the first time it is simultaneously more aggravating, expensive and difficult, not to mention the down time you experience for the car.
You live in the NE which means that unless you have a heated garage you're going to have to do all this during the warm weather when you would like to be driving the car. Unless you have a lot of worn out parts most of them should be reuseable. Consumables like rings and bearings just get replaced, its the smart thing to do.
Take the time to do it right the first time you'll like yourself and the car a lot more later.
Ed
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Apologies, I did not mean to be non responsive to the balancing question. Obvioiusly the correct thing to do is rebalance but ... If you look at a factory balance job you will discover they are not +/- 1 gram on their bob weights, they can be 50 grams or more different journal to journal. Not withstanding this apparent horrific imbalance your new Lexus idles amazingly smooth.
Get a good used O-Haus 2450 gram scale at a gun show and check your component weights if you disassemble. It'll give you a good picture of how Detroit originally put the engine together. This is not an endorsement for doing things the wrong way but maybe you do not need swiss watch precison if the engine is living below 5-6000 rpm especially if it is way below those numbers most of the time. Just something to think about.
BTW if you decide to do this, PM me and I'll send you a spreadsheet for calculating the bobweights necessary to balance all the stuff.
From your handle I suspect you are a Pilot so this next example will probably come home for you. If I look at a P-51 and do a premium rebuild on the engine I will hold reasonably close tolerances on the remanufactured engine pieces. If I rebuilt one of the GE or RR engines on a commercial airliner and built to the same tolerances I did the Merlin in the P-51 the jet engine would probably have a short service life. The engine and it probable service use in the Cobra are the same if you get my drift.
Ed