Given my recent situation, I know super cold heads and block played a roll in my destruction, I been running crossovers and no stats for YEARS with no issues, but knew certain things were set up for it, I will be setting the heads up for that but want to be safe so what works? I know if I just put stats in I will have fluxuating temps and possible water pressure issues, what will work good???

My opinion on it is this. If you want a crossover and some temperature buy the stainless marine crossover kit with the thermostat housing/ bypass and thermostat. Tried and true setup. Very expensive but it works. If you are using the regular old crossover that are mass produced in China I would set the whole motor up loose. Always better to loose than too tight. And run no thermostat. When I came to the crossroads with this dilemma I had to ask myself what is there to gain with a crossover and what is there to loose? With the question at hand I really can't see any benefit from running a crossover. I will stick with the circulating pump on the front of the motor. I know I know everyone has been running a crossover for thirty years with no issues. At the same time they have also been running them with the circulating pump for thirty years also and if you want temperature in the motor it's much easier to control with the pump than no pump.

The crossovers I have are Stainless marine, If I had regular pumps and all the other stuff I would consider that route, I am trying to make do with what I already have, when I bought the Baja years ago this was on it so I left well enough alone with no issues, I know there may be better options but I need to make what I DO have work...or just set my stuff up loose like planned and move on, just looking for more safety, I cannot do this again....

I did a bunch of dyno tests......full wet exhaust. 1 set of tests out of the many I did, was Factory recirc vs crossover. up to 5800rpm. About 2hp. HA ! Well within dyno error. Sea water pump I couldn't test because that would mean running the exhaust without water. I'm willing to bet by the massive water volume it passes plus the psi it can produce, this is the HP consumer...but nothing we can do about that.

I'm not concerned about hp or any of that, just happens to be what was on the boat when I got it so I kept it because it didn't cause issues, that being said it's playing a role in current issues, can't I get really low t stats and make it work?

I always ran crossovers with no stats in the past and never had any water temp. I have read on here in 100 places about people running stats with holes drilled in them.

I have put 140 stats with 2 3/16 holes drilled in them and a bypass to cool the headers. I am going in the water today hopefully and will let you know what results I have if you'd like. From following your posts the last few years though I will say I think we run differently - I rarely even see 4000 rpms. I believe you run a lot harder than I do....

I think at this point you should step away from the " I have to make due with what I have" and "I have to make what I have work" thinking. Your not building a 350 for grandpa's station wagon, your trying to build some pretty decent power that you admittedly are going to beat the phuck out of. Rushing it, trying to make stuff work, thinking it should be "good enough" and not paying exceptional eye to detail just bit you in the azz and its going to keep biting. Its going to keep frustrating you, its going to keep costing you money..... you need to change the thinking from "making it work" to making it bomb proof. Im not trying to dog on you Tim, Im not trying to be a dick, but Im not going to sugar coat things either. After something goes horribly wrong in the military, they do a stand down, they stop, figure out what happened and how to make it not happen again.

I run cp's high flow thermostats 120° w/ 3 holes drilled in the(3/16"),whippled charged 490 ci enginges.all the engines over 550hp get that set up.never a problem.and all run cross overs.
my friends chief 725hp engines in a 38 top gun runs no t-stats on afr 335's,,of course I did the heads,,but no issues there.before or after I touched them.

I get that but there are many guys running crossovers, with success and inwas one until recent and it's not the entire cause of my issue... May not play a role at all.... Just looking for knowing I got some heat.

if i was you tim i would be running a circulating pump.i know a crossover looks much better but imo,a na marine engine in your hp range does not need a crossover.espically in the cold water you run in.a circ pump and 140 deg t-stat will make your engine last longer.