Good morning BG and the OP (original poster) and welcome to the forum since you’re a new member.
Changing the camshaft is neither practical nor possible.
The earlier model camshafts mentioned (the higher performance types) won’t work in a 940 due to the head having the ignition distributor on the end of it. This means the camshaft has a slot on the rear end which drives the distributor directly.
If the recently purchased 940 which we’re discussing is the car I’m thinking of (QHM061), I know this car well, and it has a B230FB engine which happens to have a VX3 camshaft already. This camshaft is suited to the B230FB engine, and it has been matched by Volvo to work correctly in this engine and produce decent power output both in the middle and upper RPM range, and it works together with the 531 cylinder head which works better than the 530 head that most other engines had.
You can if you really had to, hire a machine shop to make a slot in the camshafts that don’t already have one (those early engines have a block mounted distributor and no slot on the cam) but, in your case going to this length is not what you want to do.
We can discuss certain repairs and maintenance this car needs (I think I wrote a list and handed it to the previous owner) which some jobs were urgent from what I can remember.
Better performance can always be had later.
The car is very good, but not perfect. I’d be happy to help with parts and service to keep this vehicle going forever. It can be made to go the distance and be ultra reliable just like my 940’s and 240’s that I take on long trips very often and they all have traveled well over 300,000 kilometres
