I would be leaning more towards the LSx series of motors rather than a carbie motor. Not too much more in it. Or look into a HD-T, HD-FT or HD-FTE diesel.
Alot will depend on if you're doing the conversion yourself or not. Do you really wish to spend (quite) a bit on a leaf sprung MWB or would you be better off purchasing a later model coil sprung 4B, 80 or GQ if you're wanting an ecenomical purchase.
Cheers
Corry