This is my latest effort at nailing this song down.

Oh lass, gin' ye would think it right (gin--after or before a bit)
Tae gang wi' me this very night
We'll cuddle tae the mornin' light
By a' the lave unseen o' (lave--others)

And ye will be my dearie
My ain dearest dearie
It's ye will be my dearie
Gin ye meet me at e'en o' (e-en--evening)

I canna for ma mammy gae
She locks the door and hides the key
And in the mornin' charges me
And aye aboot the men o'

For she says they're a' deceivers
Deceivers, deceivers
She says they're a' deceivers
Ye canna trust in ane o' (ane--one)

Oh niver min' yer mammy's yell
Nae doot she met yer dad hersel'
And should she flyte, ye can her tell (flyte--scold)
She's aft times done the same o'

So lassie, gie's yer hand on't
Yer bonnie milk-white hand on't
Oh lassie, gie's yer hand on't
And scorn tae lie alane o' (alane--alone)

Oh lad, my haun' I canna gi'e
But aiblins I maun steal the key (aiblins--perhaps)
And meet ye at yon birkin tree (birkin--beech)
That grows doon in the glen o'

But dinna lippen, laddie (dinna lippen--don't count on it)
I canna promise, laddie
Oh dinna lippen, laddie
In case I canna win o'

So he's gaen tae yon birkin tree
In hopes his ain true love tae see
When fa come trippin' ower the lea (fa--short for fair?--directly)
But just his bonnie Jean o'

And she's plank-ed doon beside him (plank-ed--put down with a thump)
Beside him, beside him
She's plank-ed doon beside him
Amangst the grass sae green o'

"I'm overjoyed wi' rapture noo"
Quo' he, and preed his cherry moo' (preed--unknown, moo--mouth)
And Jeannie ne'er had cause tae rue
That nicht upon the green o'

For she has got her Johnny
Her ain lovin' Johnny
It's she has got her Johnny
And Johnny's got his Jean o'

Definitions from Dictionary of the Scotish Language.
http://www.dsl.ac.uk/