Hesco toyed with the idea of producing a 4.0L aluminum block for a long time but I believe they've abandoned that project due to low demand and the prohibitively high cost of each block. Aluminum has 55% of the weight of cast iron so with a bare cast iron block at 136lb and a bare cast iron head at 60lb, the total weight saving with aluminum head & block would have been near 90lb. My fully assembled bare long block without ancillaries weighs 360lb.
Unfortunately there's no easy way to completely redesign the existing engine and even if the block/head were made of aluminum, it would still have the shortcomings of the pushrod OHV design and a non-crossflow head.
At the end of the day you have two choices. Either make the best of the existing 52-year-old engine design while accepting its limitations, or swap in a more modern all-aluminum engine. The Chevy LS1 ticks all the boxes with its compactness (for a 5.7L engine), lightness, reliability, adaptability (to AX15 transmission), easy availability, low cost, and 300+hp.
The stock 4.0L oil pan can be modified with an extra baffle, and you could also add a "kick-out" to increase the sump capacity. These measures would prevent oil starvation and reduce oil temps. Otherwise the engine doesn't need any further upgrades for reliability.