I have a 1986 +8. I will be constructing a new Conc driveway & would like to get a good idea of max rise angle the slope of the entrance can be for the Morgan to clear when it gets to the level.

Sounds like you need to get the geometry set out.

If you mean departure angle it's not that great. It will also depend on where your numberplate is mounted...

If you are building a commercial parking garage you can easily park across a 5% slope (perpendicular to the slope). If you want to build a ramp into a garage, with no parking on it, you can make it a 12% slope, but you need 10 feet transition areas at the top and bottom of the ramp at 6%. That is probably more information than you want to know, but it gives you a good indication of the possible limits.

Your 8 feet wheelbase has a lot to do with the geometry. Curb cuts are usually 5%.

On a +8 (or Roadster) ramp break over is probably more critical than approach or departure angles

We have a 2012 Plus 4 and have can not enter our garage for the break over point which is actually quite moderate. Our ground clearance problems are mentioned in several posts so I won't go into details but it has made me think about this issue.

I was thinking the best thing to do was to measure the minimum ground clearance (when two people are in the car) and make a wooden frame with two vertical pieces of wood to represent the wheels at the distance between the front and rear axles. The height of the vertical pieces is obviously the minimum clearance. Using this you can play with the aproach and departure slopes and eventualy use the frame to check everything is ok before laying the concrete.

I did what Gambalunga is suggesting before getting my 2012 plus 4, actually made a wooden frame with variable heights back and front to accommodate the variations in the spec sheet from Morgans. Make sure you make the frame long enough for the distance in front of the front wheels (not such a problem) and behind the rear wheels. In my case the rear was the problem with only a whisker of clearance. When the car arrived no problem, the back was higher than the spec sheet. I think it is luck of the draw how much they vary because on measuring new ones at the dealers they were all different ride heights.