I can only recite what I've heard about Rialtas. Wonderful little C till something goes wrong. Then repairs can be nasty. A well-cared for one could still be a good unit. Professional mechanical inspection of a used one is mandatory. I've heard of the powertrain being replaced with a FWD GM assembly. I forget whether it was based on a Buick or a Chevy V6. The form factors of those two engines is different. Buick V6 is a 90-degree block based on the V8. So, actually is the Chevy 4.3 V6, but the Chevy V6 I'm thinking of (3.3L?) is meant to be a V6 and is a 60-degree block.
Remember what I said at first. This only based on what I have seen and read. I have not owned, driven, or worked on a Rialta.