help sourcing seats required (measurements included)

Mx5 seats are popular with kit car builders as they're reasonably 'sporty' but no overly expensive.

And yes they do tilt.

I recently picked up a full set of leather, front and rear, seats from an 06 plate Hyundai Coupe for the grand sum of £40.
I will be fitting them into my Firebird at some stage.
You will be lucky to find a single MX5 seat for £40.
Basically, look around, be patient and, if at all possible, look to fit your existing runners to the donor seats.
A great many more modern seats have runners that weigh a ton with kick ups and all sorts of things that make fitting them to other car floorpans a real headache.
Ive stripped one of the Coupe seats of its runners and have still retained the tilt mechanism. I will be making up brackets to fit the Pontiac runners to them and, as a bonus ( after having had a good stare at the sellers pics and online pics before I bought them ) the rear seats look like they are doable in terms of replacing the Pontiac rears without too much grief.
Good luck!