Compost is even more effective at improving clay soil than peat and doesn't have the acidity problem or the other associated peat problems. Can I ask why you'd rather not just use compost?

But if you prefer using the peat for some reason then IMO the only way to know how much lime or wood ash would be needed would be a soil test. Lime and especially wood ash can effect quite drastic changes though IME using dolomite lime is less drastic.

But even if you know the pH of your existing soil, there is no way to know for sure what effect the peat may have or how quickly it will affect the pH without testing.

Dave

Compost alone definitely makes my soil more fertile and easier to plant in, but it decomposes and disappears very quickly. It also seems to compact more in wet weather. I was hoping a mix of compost and peat would cause a more lasting (and stable) improvement in tilth, and a steadier volume of soil throughout the season.

Unless peat varies greatly in acidity, I'd think there'd be a rule of thumb for how to balance it. Otherwise, I guess I could throw some in a bucket, add some lime until it's neutral, and then do the math ...?

I'd skip the peat and just use compost... lots of it.

Amending your soil is never a once and done kind of thing. Its something you should do continuously...

Peat moss is touted as something to acidify a soil but if adding Oak leaves and pine needles do not significanlty change a soils pH why would peat moss? As Dave and Joe have already suggested compost would be a better material to add to any soil, clay or sand, since it will have active soil microbes in it which peat moss lacks. Kip on Victory Garden has stated he likes to use peat moss to amend soils because it last so long and it does because the soil bacteria, that are making nutrients available to your plants, will not digest peat moss because it is nutrient free. So in addition to the peat moss you need to add something that has nutrients in it anyway to feed the plants you are trying to grow.

Rather hard to answer unless information on the pH of your soil, and the pH of the peat moss (are there two types, I think I recall?) are provided. And the type of plants that will be put in or grown, you may not want a 7.0 soil pH.