Hey Willo68. I have reinstated a WB factory A/C in a ute and learned a fair bit along the way. So if it helps... the biggest things for me are... use a modern Sanden compressor (the old AC Delco GM units cant guarantee to hold their gas in), install a pressure cut off switch so if gas is lost, then the compressor shuts down...and get rid of the old Holden A/C fan and put a bigger unit up front with a good cowl to move air across the condensor better.

Also look for the 1% wins like cleaning and combing the condensor fins, sealing up holes or gaps that can let hot air in or anything that limits air flow in the cabin (bad airbox flaps or controls etc).

My A/C and rad shop use a small after market modern evaporator box in their WB ute and it tucks up under the dashboard. Might be something to consider rather than the original in cabin option?

Other than all that, i've been able to make the cabin 'colder than a mother in laws kiss' during summer days, so it can work out really well. Cheers