As to the gasket, I just fitted one today. After fitting one last week and destroying it. You need to use Wellseal with these, and last week I put the Wellseal on the barrel, stuck the gasket on top, put Wellseal on the top face of the gasket, lowered the head carefully into position and bolted it up. Some of the bolts didn't go in easily so I thought the gasket was probably a gnat's whisker too small round that particular hole, poked a small screwdriver down there and inserted the bolts, torqued 'em down and tried putting the pushrods in. Oh dear. Shone a torch down there and saw that the gasket had slipped an inch towards the back! Today, a wiser Eric stuck the gasket to the head, Wellsealed the bottom face, then placed four domino-sized bits of wood on the extremities of the fin area of the barrel, placed the head carefully onto them, and examined the result, shining a torch down each bolt hole and adjusting the position slightly, inserted the bolts VERY carefully, tightend them finger tight, inserted two longer bits of wood at the sides, removed the original bits, then the two new bits, and allowed the head to settle down nicely onto the barrel. (With a clunk). So far it's looking good.