I'll tag Madkaw in a couple of hours.  He recently did a restore of a similar car and would be better able to give you a current value.

I get up too early when it gets this hot. 

 

9 hours ago, 718Miata said:

Thank you. I’m trying to decide what would be a reasonable reserve.  Thoughts?

Your auction company is charging a 20% buyers premium so that really means you will be paying for that with lower bid offers.  The car is in wonderful condition and the prices are still climbing. Good luck.

Who me ? Why would I be the expert ? 

I would be curious how a non matching numbers car does . It looks like he has the money in it, but modified , so he needs to call it a resto mod. The 70 in my shop will be a resto mod because it won’t have original drivetrain .

Value would be based on interest ,  but he should get his money back

Sounds like you have some knowledge to add to me.  That's all I was saying.  Not an expert.