Germanic strong verbs class VI

Germanic strong verbs are usually quoted in four forms
pres. - pret.sg. - pret-.pl. - past partcpl.
which has the ablaut grades in PIE
e-grade - o-grade - zero-grade - zero-grade
which in Proto-Germanic mostly becomes
e - a - zero - zero (with various embellishments)
except class VI which has
a - o: - o: - a
which is odd.

Then I got an idea.
True to my old habits I asked myself:
"What would a strong verb look like in Nordwestblock?"
So I posited:
PPIE a -> PIE e -> NWBlock a
PPIE ã -> PIE o -> NWBlock o:
and further I assumed that NWBlock had old o-grade in
pret.pl., whether originally or by later regularization.
The subsequent regularization of the pret. in the
Germanic languages (by ex-NWBlock speakers) might
evidence of that.

Now did NWBlock have a/o: ablaut?
Possible evidence:
English hook, Dutch hoek, German Haken
English hood, Dutch hoed, German Hut, English hat
(connected by Kuhn to Latin cassis "helmet",
further Chatti, Hessen, examples of -tt-/-ss-).

Then I stumbled over some Friesian strong verbs
(and what could be more NWBlock than Friesian):
pres. drank-, pret. droonk-

?!?!

Who could ask for more?
(Except I'd like to ask the list for more
information on Friesian verbs, one verb is perhaps
too little to build a theory on).

So the proposal is:
The class VI strong verbs in Germanic are loans
from NWBlock, with the characteristic ablaut
pattern of NWBlock.

Afternote:
I noticed that some of the class II verbs
(eu - ou - u - u)
are instead
(u: - ou - u - u)
eg. Dutch
schuiven "shove",
duiven "push",
zuipen "sip, drink"
which have all been singled out by Schrijver as
glosses from his substrate "language of geminates"
(geminates BTW being a feature of NWBlock,
according to Kuhn);
perhaps the 'u: in e-grade' verbs are also loans
from NWBlock?
(According to Wikipedia group II "has grown"
in Dutch, but maybe it was just bigger in Dutch
to begin with than in other Germanic languages.)


Torsten