I'm in the process of purchasing a 27hp prodrive (2004). I'm adding the reverse plate and the pin puller, but there isn't a tension knob. Do I have to install it, or can I go without it? How difficult is it to insert the bushing and tap the housing?

You can go without. I have a bolt in mine. If you keep it greased you won't really need the tension knob.

Any idea what the holes are for on the back of the captivation plate?

holes on back of the cavitation plate are usually used to put a rope/strap when trailering. i couldn't see the holes in the pic.

you don't need a tension knob. i never had one.

just my opinion, but the pin puller is garbage, u don't need it. you'd be better off getting kicked in the nuts.

good luck!!!

The pin puller Preston made for me works like a champ..

mine ain't from preston. some other guy. i threw it in the trash.

i hadn't heard from preston in years, he makes nice stuff.

Added better pictures of the holes in the captivation plate. Future ideas are to mod a sleg like bayou boys and maybe purchase the weed cutter. Next thing on my list is to get a transom saver modded to get the prodrive home

that style of cav plate came with them holes. lots of people threw a black rubber strap from the hole to the rear boat handle to keep motor from swinging while on trailer. i realy think they were just there from machineing the cav plate, i don't think they have a 'special purpose' i could be wrong. lol