Welcome aboard. Whether you are looking to do the upgrade to 40A yourself or have a shop do it, the documentation on this forum alone could take you a month of Sundays to read it all. The resources here, in addition to upgrades, cover everything from final drive R&R to coolant hoses and valve shim adjustments.
I bought a 91 with 32k miles on it as the 4th owner. The thing looked like it had come out of a time machine with it being garaged it's whole life. If there isn't documentation of coolant, fuel hoses, timing belt and other scheduled maintenance, you're in for a bit of a pull apart to do it, but it can be done. I did it 3 1/2 years ago at the 45k mark. Replaced a bunch of rubber that was pretty calcified. The engine is interference, so if the timing belt were to break,the valves can collide with the piston. The timing belt has shown a history of being quite hearty, you can get the automotive Gates version for more than half of the cost of OEM, to help save money. I did, and have over 30k miles on that belt.
Whatever you decide, for who does the work, there are plenty of us here that will be helpful to you.