For details on the Hurth failure see my (alas, lengthy) post of today's date on the C36IA Cruising form. I describe the symptoms in that post.

I received the new PRM120 this morning and immediately celebrated at Tim Hortons, the essence of what is Canadian.

It's striking how much beefier the PRM120 is. The M35B's 35 hp 36 will be demanding a considerable less percentage of load from the PRM, compared to the demand on the lightly built Hurth,

The first 'unknown unknown' I discovered is that the PRM120's output hub in NOT notched. There's so little room to slide the prop shaft aft on a Catalina 36 Mk II that the cutaway of the hub is crucial to removing and reinstalling the transmission if ever maintenance is needed...even the small Hurth. Without the notch in the hub, I will need to install the transmission on the bell housing and put them in place as a complete unit - not an optimum solution. Tomorrow first thing, I will take the PRM120 to the local machine shop to see of they can machine a notch into the hub while retaining the balance of this rotating component. Unlike the Hurth's hub, it appears that the PRM hub can be readily removed. 

Paul, there is NOT enough room to move the prop shaft back that far. That's why I had to move the engine forward 1".

Got an elegant fix for the exhaust riser; no need to move the muffler.

Unless someone needs the writeup soon, I'd like to wait a month or two to write an article for the Technical Upgrades library. I am absolutely whacked (!), and I MUST be making miles to the south. I have about a thousand miles to go to get back to PDX. This was a helluva job to be done in a remote location, in the slip, all by myself except for a wonderfully creative machine shop a block away.

The boat's ready to go, and I'm planning to depart Prince Rupert tomorrow about 0630.
 

Update: 9/18/17 Comox, BC. 

Almost 400 nmi on the new PRM120 and it's working well. I hauled in Campbell River for a re-pitch of the prop, from a 10" to an 11.4", needed because the ratios are different. The Hurth is 1:1.79, and the PRM is 1:2.00. 

I found my bottom paint was fine (Pettit Trinidad SR hard), the zincs were fine, and there was a hairline crack and tiny, tiny movement when I pressed on the shaft strut. I was going to inject epoxy into the strut area, but the crack was so small it was impossible t do so. I'll address that in the future, if necessary.

There are tradeoffs.

I'm still digesting the new installation, and I have another 400 miles to get home to 'absorb' the reality of it. But my brain is so fatigued from this lengthy (mostly solo) trip that it will be some time before I can write it up. If anyone is considering this step short term (instead of in 2018) they should call me or PM me for a personal assessment.
 

I am now home in PDX, and have almost a thousand miles on the new transmission. There are many things I like about the exchange from Hurth to the PRM, and I will address them when I have time. But for the moment I am cautioning other C-36 owners to call me to discuss if they are considering this transmission changeout. 

I'm not yet completely happy with my installlation.

There is a noticeable engine vibration that is of higher amplitude than the original installation. It's especially noticeable at idle, but tends to get subdued as the RPM gets beyond 2,000. I have deduced that the vibration is the result of moving the engine forward by 1 inch. There is insufficient engine bed to accept the most forward mount lag screw. The new location of the forward engine mounts necessitated that a new method of attachment of that mount's forward lag screw be fabricated. I designed a 3" x 8", 1/2" thick steel plate that utilizes the existing mount holes and adds a couple more lag screw points aft of the forward mount, that accomodates the forward attachment with a bolt into a threaded hole that 'cantilevers' beyond the existing engine bed.

(This UPDATE is a copy of my repsonse to Bill Miller's PRM thread for the Mk I series boats.)

This summer, after two Hurth failures, I replaced my Mk II's transmission with a PRM 120. The 120 is 1-1/2" longer than the Hurth HBW 100, requiring me to rebed the engine 1" forward of the stock location. It's a fine performing tranmission, but I am not completely satisfied with this mod; plus I still have a lot of woodwork to accomplish to replace the temporary 2x4 spacer I installed that moved the engine cover and companionway steps forward by 1". Bill's research opened my eyes to another possibile transmission that seems to make for a 'more elegant' installation on the Mk II.

Mk II owners can 'stay tuned' for more details. Once the warm weather returns to PDX I will attack my project again. Thanks to Bill Miller, I'm now considering a PRM 80 or PRM 90 as a potential 'right' transmission for my boat.  

UPDATE: Today I ordered a brand new PRM 90.

This is the transmission that I SHOULD have ordered when I had my second Hurth failure of my Inside Passage trip this past summer. However, I was unaware of its existance at the time, and the PRM 120 was immediately available in Canada.

With the smaller PRM 90 I can move the engine back to its stock location, and I will avoid having to modify the engine cover and companionway steps. Once the weather warms up here in PDX, I will get on this project and write it up for the Technical Upgrades Library.