If you want to do a hex conversion on the front you'll most likely have to buy a roller for parts, or mod something to work. The stock 7854 hex axles are just not out there. I'd look to Pro2 SC10 eBay chop shop caster/steering blocks/axles to install. This is what the SC10 users are doing....
I personally have not done the swapping of the "5 series" caster/steering blocks & axles on the "4 series" T4, but the eBay chop shop for such parts is here... https://www.ebay.com/itm/313306544277
Just be aware the ball studs are larger, and would need to account for that as well.
I'm not sure what your intensions are for your T4, as parts supply is very hit & miss. If wanting to race the truck, then find out what classes are held before choosing an electronics package. Also, I'd start looking for spare CV bones/dog bones, axles, idler gears, etc., etc... some days you can get lucky, and can have them jump out at you, other days... not so much.