Advice regarding stray cat,please.especially if u have experience with semi-feral.?

i have 2 friendly cats.a neighbor moved and left behind a siamese mix.we fed him for 3 months and finally caught him and took him in.he loves our other cats and they love him..we are going to keep the new cat,indoor only like our first two.heres the problem.sam the new cat has an appointment to be neutered/get shots this thurs.but he does not like to be handled,and he hisses and is threatening when we try to pick him up.i would like to have proper vet visit for him,but he is a large scary tom and i am afraid my husband and i will get torn up trying to catch him.we had to use a trap to get him inside and i think he will be too smart to fall for that again.his urine does not smell strong,unlike most intact males,and he goes in the box and does not spray.i wonder if he has been fixed already-cant get close enough to find out.we dont mind that he doesnt like being handled.he gets along well with our kitties,and he was not looking too good on the streets.we are glad to give him a home, even if he would rather interact with other cats,not us.he is not aggressive unless u try to pick him up or carry him.he will let himself be petted sometimes.but he does get agrgessive if handled and messed with too much.so,do we try to wrestle him into the carrier thurs morning,put it off awhile,or just not neuter him? i worry that intact males are prone to blockages, however.i am not trying to get out of a vet visit,i just dont want to get hurt,my mom was bit by a cat once and had to go to the hospital it was pretty bad.we could not leave him outside,other cats were beating him up ,he seemed miserably unhappy.except when handled a lot,he seems content and happy at our house and relieved to have fresh food,water and a nice place to live.so-do i try the vet thurs or not? hints or tips for dealing with fearful,semi-feral cats,appreciated...