You're not going to have any problem finding manifolds or a coupler since Volvo still supports the 454 installation. The major problem with that model engine was the ignition and EFI (if installed, since theres also no parts available) You have the ignition solved since the previous owner did it the only way it can be fixed: Replace it with a distributor (they also put that same ignition on the 460 for a year or so.....I sold the dist from my previous 460 to a guy locally that had one....he had no way to fix it at all.)
It also will not have the same shift cable problems, ESA and dog-clutch problems since it's a "CONE" clutch drive. Although not exactly the same as the newer Volvo Penta drives. It was the "test" system if you will, for Volvo's current drives. (OMC WAS the designer of those drives (during the partnership with VP) Then they just sold the whole mess to Volvo before they went out of business. The VP SX drives were the result of the partnership.....They're still developing and improving them.
By the way.....all these drives are tied together in one form or another...... A Kiekhaefer Engineer was the original designer of Volvo's first drive. (And OMC's drives too.) They all at one time worked for Carl Kiekhaefer (Kiekhaefer Mercury)
http://www.rbbi.com/folders/pat/isd.htmIn any case, If you want a Liberator. and you wanted to repower the newer OMC one, you could easily install a Mercruiser Bravo gimbal and drive behind that 454. You would need to remove everything and obtain a complete package (less the actual engine) You could also install a Volvo Penta gimbal and drive. (I'm not sure but I think Volvo has a kit for putting Volvo drives on OMC gimbals.....I'm also not sure about that particular drive/gimbal since it's different from the previous models that the kit was aimed at.... There's enough boats that are using the "interim" OMC drives out there that you could EASILY sell it.
(I got around $1400 for my 87 model Dog-clutch King Cobra drive) I also sold my 460 flywheel housing and inner transom plate for about $400 to a guy in calif who had the coupler literally explode and destroy those parts...Before he talked to me he was ready to scrap the boat since it wasn't worth repowering. (The 460 flywheel housing is not available anywhere at any price except from a boat being disassembled) All totaled, I got a little over $3000 for the everything on the back of my 87 Lib. and I still have 2 SS props, the power steering stuff, and the rebuilt carb/flame arrester (if anyone wants that stuff!!)
There is another reason to get any boat with a Mercruiser nowadays......If you like to do your own work or scrounge parts (which you might have to do with any OMC drive) you may want to stay with the system that has the largest amount of used and aftermarket parts out there. Go to EBAY and do a search in "BOAT PARTS" for "VOLVO" and another one for "MERCRUISER"
On any given day you'll find 3 times more parts, drives, etc for Merc over Volvo. (Right now it was 3084
to 823) For example, there's a guy over on iBoats looking for a Volvo Gimbal. (his was damaged somehow beyond repair)
An ebay search for "Volvo transom" produced about 30 with 10 actual transom assy's
A Mercruiser search produced over 100 hits and more than 25 complete transom assy's new and used.
I like the 86-89 Liberator "look" over the newer ones so if that one is in otherwise good condition you might consider it....and you might get it fairly cheap.
In either case, make sure you have someone that knows what they're doing inspect it carefully.