Probably better to scale down the canopy on the US Navy's two-seater TA-4 trainer. That way the pilot's seat back could be closer to the centre-of-gravity, but you still have a large enough exit hatch.Starting with one of the TA-4 might help, as it would give a larger canopy to start with or one of the Singaporean TA-4SU as they are actually longer.
If you kept the slats, one could go with manual slats to solve a heap of aerodynamic development issues.
On a replica, landing gear only has to be half as long ... as long as you skip carrying bombs, drop tanks, etc.
Also re-read some of the books about Ed Heineman to understand how he was able to build A-4
Skyhawks so much simpler and smaller and lighter than 1950s vintage competitors. A-4 was so small and landed so slow that it was one of the few US Navy jets that could operate from British, WW2-surplus aircraft carriers like those sold to Argentina, Australia, Brazil, Canada, India, etc. The Royal Canadian Navy trialed A-4s on HMCS Bonaventure, but never bought any as by then the RCN had decided to concentrate on anti-submarine warfare.