Still doing research, I REALLY like KCVALE's electric one. Working on getting fenders from Big O Manufacturing at the moment.
Hi Gordo, welcome.
What a score on the bike, two for the price of one!
You really don't want to try to direct drive with the disc brake and 7-speed.
A 66cc slant head (with the head rotated 180 the so plug is in front)
should just fit centered if you use a SickBikeParts.com shift kit and make your own offset carb intake.
It is much more work and money but should make for a kick ass ride.
As you seen I went electric on my Dolomite but that was ~$1500 just for battery, charger and electric motor kit, but you can gleen some insight to what is involved.
If I were to do a stroke on it I'd start with the SBP HD shift kit, it has the good freewheel.
http://www.sickbikeparts.com/catalo...ducts_id=86&osCsid=hsi4nkod9s3hnsk1cmkgq3fhg7
$200
There is a form for ordering, the 2 important selections are the BB Adapters and seat post diameter.
Seat post diameter is 1.25" (32mm).
You don't need the BB adapters, the BB is threaded but not very far in, but that's OK as it's not a cartridge shaft, just bearings and screw in cups.
You will want to get a crank removale tool if you don't have one however.
The frames BB is 110mm wide. Thankfully sickbikes now carries them, I had to fashion my own on the electric.
http://www.sickbikeparts.com/catalo...ucts_id=214&osCsid=hsi4nkod9s3hnsk1cmkgq3fhg7
The front tube is 1.8" (45.6mm) wide so you will need a new front mount as well.
http://www.sickbikeparts.com/catalo...ducts_id=85&osCsid=hsi4nkod9s3hnsk1cmkgq3fhg7
Select the 1 3/4 to 1 7/8 bracket with 1.6" stud spacing unless you have the one odd engine with a wider front.
You can orient the bracket to bend up and forward for the best grip.
You might as well grab a NGK BPR6HIX spark plug while you are spending money, it's a colder weather plug.
http://www.sickbikeparts.com/catalo...ucts_id=111&osCsid=hsi4nkod9s3hnsk1cmkgq3fhg7
And don't forget the dual pull brake lever.
http://www.sickbikeparts.com/catalo...ducts_id=41&osCsid=hsi4nkod9s3hnsk1cmkgq3fhg7
That will get you started on the right path, or at least what I'd start with ;-}