Oodnadatta to Finke can be pretty harsh on tyres from the rocks and when we did Finke to Alice there was a lot of bulldust too. You'll need to allow at least 2 days as even if good conditions your speed's not going to be high.

Whilst I don't think it's a potential no go, the other option is to go accross to the hwy as you say and to this end the Painted Dessert is worth a look and this then takes you out at Cadney Park Roadhouse. Bit of a backtrack as the more direct route is on to Marla.