1: A Cummins is a good idea, the truck would rock with a R2.8 in it. I could do it but am busy as mentioned before. My buddies over
@Delta VS could easily do it and have done one before.
2: I am not a fan of throwing a lot of money at the 1FZ. You got one that is going to be hard to smog for a lot of people as well.
If you got the money to throw at the truck, I strongly suggest putting a 1HDT in it. You can still keep the H151 trans and the tcase. This truck well sorted with a 1HDT in it is easily worth $35k+.
A cheaper option that would be even more fun to drive would be a v8 swap. But I think you would narrow who would pay you good money for the truck.
Part of the problem with what you are selling is that it is a regular cab pickup. Anyone who needs a Cruiser for family use is not a potential buyer for you. So it is a small market but, very very few 70-series pickups are in the USA and even less are available to buy so it is simply a matter of finding that buyer. I have done very well with Craigslist myself but you have to be willing to sift through all the spammers.
GLWS and Cheers