yeh, the original mounts have been hacked off, re-shaped and remounted in the correct place..
rear mounts are all new too, dont have a stock L frame here to compare dimensions, but they are different.
i guess the rear mounts were done first then the engine was bolted to them which gave the position for the fronts..
been looking at the H frames i've got though, and i reckon it'd be an easier job to convert an H, mainly because the front mounts only bolt to the ally frame anyway. but there is the crossmember on the H which may be in the way.
this is another 4/6 i found a pic of, mounts look way better than mine
but, seems the engine in that is further forward, there's no way in hell the sprocket cover will fit on mine, and i reckon there's already too much weight on the front. so god knows what that one rides like. also, notice how close the rad is to the front wheel ? and how the titchy rear sprocket brings the chain runs a bit close to the swingarm ? only way round that is bigger sprockets front and rear. fortunately 520 front sprockets are readily available for the 6r lump, so you can run those, plus 520 chain and stock zxr400 sprockets at the back, and renthal go from 38-52 (?) rear and 14-17 (?) front.. for mine i think 16/42 is about right, but it depends on exactly where your drive sprocket ends up being located, and what state of tune the lumps in.
Brian from AMS put an 'F lump in an H a number of years back, and is still working on the 636'd L, he may be worth a call when you get nearer to starting.