go fro it man, woudl be bloody awsoem, even stokc l20's get going allright especially in a tiny little rolla, if ya can get all the aprts liek engine, box mounts bit of tail shaft and all that gear it wont take much to chuck it all in and you could do it really cheaply, the only problem you might run into is the height of the l20 due to increased stroke, nothing a bit of a bulge in the bonnet cnat fix, and you may eventually decide to go back to an l16 or an l18 and they should fit fine height wise
just my 2c