You don't have to spend a fortune to get some positive results. A '72 142S should have HIF SU carbs. They are fine. To get more oomph from your 2 liter - raise the compression ratio and install a healthier cam. I think your stock compression is something like 9 or 9.5 to 1. If you mill the head 40 or 60 thousandth of an inch that will bump the ratio to around 10.5-11 to 1. That depends on the starting ratio. I think the "green book" lists the head thickness (for lack of a better term at the moment) - that is -- from the head/block mating surface to the machined surfaces on top (head bolt or valve cover machined surfaces). That thickness will determine the compression ratio. I found when rebuilding my B20 that for every 20 thousandth taken off raises the ratio about a half point.
On my engine I went a bit further and found a carb type cylinder head (maybe from a Canada car?) that has the 44mm intake valves (like a Fuel injection head) over the normal carbed 42mm and did some minor porting and port matching on the exhaust side. You don't need any kind of wild cam - the "K" cam works well with carbs. The split exhaust manifold may not look sexy but is very efficient. A switch to the later Bosch electronic distributor or a good aftermarket will be a plus. I wouldn't go for any radical boring - at the most that will get you a few cubic inches - but make the block un-rebuildable. A few simple changes can get you from the original 118hp up to about 130 - something you'll feel. Good Luck with your project. - Dave