Lovatts Holiday Collection 96. Giant cryptic

letter count please...some of us don't have the actual puzzle
75a KEEPER ?

75 a. Turned out to be gamekeeper. I hop.
Still having bother with
61 d. Initially adults only located in museum tomb. 9 letters. My guess is it may be mausoleum as I have ....o... but can't seem to get words across either.
77 a. Register alternative Verne theory. 5 letters.
Also 12 d. Most punctual member trapped in protest. 9 letters. I have p.o.p.est

mausoleum
enter (verne theory)
promptest

Thanks a lot - did manage to think of that over'nite