Yes, you should be able to deflect the belt about 1/2"(?) when pushed in the middle between the 2 pulleys with a thumb. Make sure you know whether the pushrods are chromoly (adjusted to "loose 0- there should be no play but the pushrod will spin in between your forefinger and thumb) or aluminum (.006").
I've read that if you have a 2nd set of valve covers and a junk head (with bail), gluing the stock cork gaskets to the covers with (iIrc) contact cement or permatex makes them pretty leak-proof (and they won't move around).
Make sure the car floor pan is close to level (front to back) when draining trans oil. It drains quickest when the oil is warm (just after a drive) and I've read to let the oil drain until there's 20 seconds between drops. From the Bentley manual- "If you attempt to fill the transmission too rapidly, the oil may overflow and give the impression that the case is already full. The manual transmission requires 5.3 U. S. pints (2.5 litres or 4.4 Imperial quarts)." Give it time to flow into all the nooks and crannies. The level should be up to the bottom of the fill plug, and don't forget to wipe the fur off the magnet on the drain plug before re-installing (make sure the drain plug gets fitted first!). Also from the manual- "The hypoid oil should always be changed 600 mi. (1,000 km) after rebuilding the transmission". Normally there is no need to change trans fluid more often than every 20-30,000 miles.