Hypothetical 360 magnum build

I might be buying a replacement for my either my 01 Durango or my 96 Dakota tomorrow.
Found an 03 Durango RT that supposedly needs a motor, I rented a tow dolly and am going to look at it tomorrow early it's cheap and supposed to have a very clean body and interior. If it isn't as advertised I won't be getting it.
Being an RT it's guaranteed to be a 360 and not a 4.7.

I've asked this elsewhere and discussion has gone sideways.
No "find another" response.
No " what happened to" either engine
What I have is what I have.
Yes I know that the engine in this thing might really be alright, it's 90 miles away I haven't seen it myself yet.
But the idea is to use what I already have here if possible.
I have a 00 short block here that was a doomed rebuild. Less than 3 hours on it and between a set of "ready out of the box" EQ heads that weren't (valve guide clearances were way too tight) and a stuck wide open injector or 2, it ended up with the break in oil coming out a silvery slurry.
That and a melted, glowing red magnaflow cat that was put in brand new with the rebuild.
Plans are to re rebuild this 30 over short block to be able to make lemonade out of lemons so to speak.
It has a set of speed pro stock replacement coated hypereutectic pistons in it now. At a minimum it will need rings and bearings again. Don't know yet what else.
First question is HOW different is the external balance mismatch between a LA and a magnum?
And where? Pistons rods or crank?
Reason I ask is I have a set of speed pro or sealed power 30 over flat tops for a LA 360 with only valve relief eyebrows in the tops.
For starters I'm wanting to use the LA pistons in the Magnum block. Possible? Feasible?
goal of engine is hopefully "some" mpg improvement vs the stock 360 that's in the Durango now. Improved torque for towing the camper. Being an RT means 3.91 gears. Has a 46re behind the engine.
also I have an old but brand new MP "RT+10" cam that was "current" in the OBD1 days.

on the heads I'm kicking myself for not going after the nos factory new magnum heads I saw on CL earlier this year. For $400 that was a deal in my opinion. I have 1 known good factory magnum head here. I have 1 more candidate here that needs checked.
the engine in the possibly new to us Durango has its heads. But supposedly the reason it needs an engine according to the seller is it overheated. So doesn't bode well for those being any good.
again I haven't seen it for myself, I don't know yet.

failing that I'm going to need some heads for it. I want to run no more than 89 in it, will be a daily driver. Not looking to race, probably won't see over 3500 rpm. Do these speedmaster ones that everyone is talking about come in a magnum version? I cringe on those because of the Chinesium content. How bout Edelbrock? So they?
just spit balling at present/ main question I need answers for have to do with those LA pistons in magnum block, mostly having to do with engine balance. They are currently still attached to LA rods. I have yet another set of magnum rods here that I could switch them over to.