As to the urethane vs rubber, I concur with
@saforwardlook on his orientation. I came to this conclusion decades ago regarding my '77 Camaro (which one of my friends, who had a '78 Z/28, said the "F" in GM's F-body designation meant "flex"). At the time, it was a popular modification to put solid body mounts on the Gen I (1967-69) and Gen II (1970-81) cars to "tighten things up". I'm thinking that with those solid mounts, it would transfer forces into the body where they were not meant to be, so that was not good for the body structure.
So, my orientation became that if the rubber was at a pivot point (as upper control arm bushings), that might be a good place for the urethane bushings. But where many people put them on race car chassis was on the lower control arm bushings, for better "location" and less deflection under load. Which WILL affect how much of the road is felt inside the car. On a race car, such feedback can be desired, but in a street car, NOT.
As to body mounts, the bottom part of the mount can be about "location", but the upper half of the mount is about "insulation". So the bottom can be urethane, as the upper part is rubber.
ONE place that urethane is advantageous is on the link bolt grommets at the end of sway bars, where they attach to the lower control arm on GM front suspensions, for example. The addition of the polyurethane bushings makes the bar act 20% larger than it would with rubber grommets. And they are inexpensive, too! The white GM grommets are stiffer than the light blue ones that Moog sells in their kits.
Now, one reason that people now feel their Chryslers are sloppy in handling, when they were new, to be firm and not sloppy. With a firm, but compliant, ride. GM's were "soft and sloppy", by comparison. Fords were "soft and understeered".
So, all things considered, stay with the good quality of rubber bushings and such. KYBs are supposed to be about 25% stiffer than stock, so that will compliment things, too. Then keep the tire pressures in the 32psi range for P-Metric radials.
As for "more caster", not needed. Reason is the Chrysler front suspension geometry. On the GM cars it really works on, when the chassis leans into a corner, the tires lean with it. On Chryslers, the outside wheel goes into negative camber as the inside wheel goes into positive camber, which means that as the body leans, the wheels become more perpendicular to the road surface, so the outer wheel's sidewall is better braced against cornering forces. THAT is the key to why they have better steering response. On GM front suspensions (as my Camaro has), adding caster into the mix gets to the same things as the Chrysler front end has had, by design. Too much caster can also cause the outer tread ribs to wear faster, too, as the car chassis stays flat, yet the wheels camber more than normal in turns.
Just some thoughts and experiences,
CBODY67
