There is another way guys, as Brad says, do it on the floor first, the top 2 bolts align perfectly, you just need to enlarge the top right hand hole in the gearbox to except the larger locating dowel (that the bolt passes through),Sierra is 13mm Vit is 15mm ,easy.
On the bottom, the Vit bellhousing is wider than the Sierra, and so is the bolt pattern, each bottom bolt is now about 20mm further out, the weld on tabs are one way to go, but it means you have to get it welded again when you shit a G/box or have your's rebuilt
the other option is, do the top as above, bolt it together and run a drill through the gearbox holes into the bellhousing mouting flange on the engine, there is plenty of meat to accomadate these holes, but you must make a type of crush tube as the nut dosn't have a flat surfase to pull up on.
This crush tube (for want of a better term
) is made from a tick walled tube that is cut at right angles to tube on one end (where the nut and washer pulls up agianst) and cut on an angle on the other (to match the angle of the bellhousing mouting flange) this looks very neat if done carfully and is moocho strong.
The other thing to address is the sump and pick up, this is easier to work on if the engine is inverted on a stand, you will need a 1.3 sump, a 1.3 pickup and a 1.6 pickup.
Fist the sump needs a bit of a LIGHT carress with a hammer at the rear main, you will work it out, next take the 2 pick ups and look at them carfully, on mine I cut them in such a way (about 1/2 way along the tube)that the 1.3 tube slid inside the 1.6 tube (or was it the other way around)and made a realy good weld, mine was that tight I could wedge it in there and adjust it to the correct depth before welding, you will have to cut a bit of baffling in the 1.3 sump to clear the new pickup.
Another thing is the starter, allow 2 hours with a die grinder and a large piece of chalk
This is not a bolt in conversion (few are) but one that is well worth the trouble you will be wrapped in the cars performance.
Peter.