Engine What a Conundrum we find ourselves in.

I'd say your rods are fine for what you're looking to do. In my engine I still use the stock sized rod bolts as well, so you'd probably be fine going the same route, but it NEVER hurts to upgrade those if you want. As for the pistons, I'd go with a flat top hypereutectic piston, no need to go forged for what it sounds like you want. Again, it also depends on what your block needs done. If it needs bored you'll need to replace the pistons anyway. If it doesn't need bored the original pistons would be fine unless you want to change compression ratios - which a flat top piston will do that for you most likely.

Higher compression will give you more power, so it's good to a point. Flat tops won't make it so high you can't run even 87 octane in my experience.

I don't think you'd need machining on the block for a retro fit roller lifter set, but I'm not sure on that as I have no experience with it. I believe the solution to that was longer lifters with tie bars in order to keep the rollers going the right direction on the cam and not rotating like standard hydraulic or solid lifters do.

The advantages of a roller cam and lifters is that they can have more aggressive ramp rates vs standard lifters. I believe there might be a YouTube video on the ins and outs, but I'm not sure about that either. Basically it's like rolling a wheel along a bumpy road vs using a sled - if that makes sense. The roller lifter will only contact the cam lobe at a single point theoretically whereas a standard style lifter has a flat surface riding the lobe. Roller cams also have the advantage of not wearing as fast as a standard cam/lifter set. I guess the choice is yours on which you'd prefer to go with, neither will be a horrible choice. But since it sounds like you want a relatively tame engine and not some screamer, the roller cams will only really give you the benefit of less friction and longer life.

It really comes down to cam specs when it comes to how your engine will behave. Cam specs are kind of like voodoo to some - and I'll admit that I'm no guru! I'm STILL learning about cam specs and how they affect an engine. But you'll probably want a wider lobe separation angle so you have vacuum to operate things like power brakes. Something like I suggested which had a 112* LSA provides good vacuum. The more narrow the LSA, the more choppy it sounds at idle and the less vacuum your engine will produce. That's because the exhaust valve isn't closed as much when the intake starts to open. So a cam with something like a 108* LSA will produce less vacuum and have a choppier sound at idle if all other things are equal. Comp Cams has probably the easiest to follow chart vs most websites that try to explain it all:

Here's another site that kinda keeps it short in it's explanation:

But, in the end and in your case, I think it's going to be a cost vs gain comparison. And again, if it were me, I'd just stick to the standard hydraulic lifter and cam. In my opinion the cost doesn't justify the swap for what I think you want to accomplish.

Yep, like I said, I don't see a benefit for what you're looking to do vs the cost of the components.