Puma will go in with very little work aside from wiring.
I know that both and both offer a 1.7 Puma transplant for a price. I think your basic reconditioned engine from them on average comes in at about £1800 (Fitted).
The only problem is, that if you want a brand new engine, it's gonna cost more, and don't even think about getting them to put an FRP engine in, as the units alone are £3000.
There are some less pricey options though (One being sourcing the engine and doing it yourself).
The second would be to go for the less powerful Zetec S engine.
The 1.25/1.3/1.4/1.6 Zetec S/1.7 Puma all share the same sort of engine dimensions and the same engine mounts.
The Puma is essentially a bigged up Fiesta anyway, and the engine bay is amost identical (The blocks just a bit bigger).
Also, when thinking about a bigger engine, you're gonna have to factor in gearboxes aswell, the putting a 1.7 engine in with a 1.25/1.3/1.4 box will soon find you running out of steam
Hope that helps a bit
