I use a trolley jack. Center of rear crossmember in back and center of lower crosshead tube in front. I do not use a piece of wood. I just let the jack scratch the bottom of crossmember and tube. IMO not worth the trouble. However I temporary I put the jack stands under the ends of the chassis in the rear and the ends of the tubes in front. If more than a few minutes I put the jack stands under the rear axle at the end near the wheels to prevent "kick up". If I had a new or very nice Morgan I would use the wood. I envy those that have a hoist or use of one. Way to go!
I don’t use the timber blocks to protect the cross member from being scratched, I use them to spread the load, and avoiding the jack from slipping off ! That’s why my blocks have the V shape where the cross member locates, with the under side of the block routered out the same diameter of the jacks lifting point