There are only 3 good headers for the small block , TTI , Dougs & Hooker 5115 , all stay above the steering link & have good ground clearance if you want to use headers .
318 manifolds don't flow well But the later 92 up Magnum manifold do & should be able to locate easily in wreckers or online...
SJ Or at worst SL is the only oil to use , ZDDP is more important than the weight , Agricultural oils from farm supply are all SJ as they are off road use .
the engine clearances are generally created for a given oil , more clearance for heavier oils & tight for lighter oils , I typically used...
E bodies should have the 130 tooth flywheel & alum belhousing , these came with 10.5" clutch for light duty & 10.95 in HD applications the 143 is fine should have the cast iron belhousing , I would use an 11" clutch on any 143 tooth flywheel .
That clutch doesn't even look like it was working...
I have experimented with porting a LOT over the years but I don't have a flow bench , just time slips !
the motors I build Always run faster than they should ...
Anyway you will see some gain raising the ports for sure ... my $.02
Where I have made serious gains tho & messed with people on...