I just got don't doing one a couple months ago on a mk1 spitfire.
Let me try and describe how I did it.
The first thing I would do is make sure it is a warm day so the top is stretchable. I would leave it in the sun for 5 to 10 minutes.
1st I put medal bars in the front
2nd Put the top on the car, make sure the medal bar is pulled all the way in
3rd You should have 2 snaps on the ends of each windshield top area. Get someone to help you stretch the top tight across the car and with a fabric marking pen mark one side to do your snap in. Take the top off and punch your snap in. Put back on the car, snap the one side and now stretch the other side and mark for snap. The tighter the better and also the tighter to get it into the channel the better. I found mine will sometimes come out of the channel and then only the snaps are keeping the front of the top from flying off as I drive. So it isn't just getting the top tight across the car but also pulled back tight in the windshield channel.
4th But the back metal bar into the top
5th Put the top back on the car with the bow in place. Snap the front. Put the back bar into the 2 back brackets. Unlock the bow so it springs up to the top position. Make sure the bow is fully extended with both cross members pulled all the way out. (the primary bow and the one that folds up)
6th Now center the top right to left. Now try and stretch the top right to left and pull down on the bottom by the bar so you can see were to put the next 2 snaps. Work from inside to outside. ( you may even what to lock the bow in the down position to maybe get a little more play. Tops stretch with time and temp) Mark the next two snaps , take the top off and insert these 2 snaps.
7th Put the top back on again and snap everything down and stretch top again to mark the next 2 snaps. Do this over and over until you get all snaps in place. Work from inside or center to outside of car. I did 2 snaps at a time. 1 on the right side and one on the left side.
You are almost there:
8th I had to get more snaps at this point, I wanted to take the top off the bow so I used 4 snaps on the fabric inside the top that you will see goes round the bow.
9th You will see 2 stretch cords with fabric sewn on the end. These snap on the bow. You should see a couple snaps on the locking arm. With the top on you should be able to stretch the cords back and see here to mark and insert these snaps.
10th Now you will find to pieces of bent thick round steel, made in a long u shape with curled ends to receive rivets. These go at the front of the top on the downward facing part that your window sits against. They are meant to sit in the weather seal so when you roll your window up the flap will stay on the inside of the window not the outside. I tried to use the snaps they gave me but they didn't work out very well. I am going to the shoe repair guy to get some nice black hammer type rivets to use. This is hard to describe sorry. Maybe some one can send a picture or PM me and I can try and walk you through this and anything else you need help with.
Now after putting the top on and off 20 times and replacing several rivets because you didn't get them put together quite right you will be done. Good luck.