Nice mods! Will certainly be pondering switching to a grip shifter for my rear hub on my brompton too! And keeping an eye out for old MTB bars..... XD

One thing i'm a little skeptical about, is the use of skate wheels to replace the rollers. Is there a tendency for your heels to clash against those? I had a friend who did the same mod on his P-type brompton but often found his heels knocking into them....