Spark plugs,are these the right ones?

[ProfitOfDoom]

I just went up to my local boat shop and told him what engine I had "mercruiser 454" He gave me plug that are NGK R BR6FS and I just pulled out the old ones and they say AC Delco MR43T.
They look the same at the bottom threads but the new plug seem to be shorter,I know there not the same but can they be used or should I not even bother and just go find the exact plugs? I didnt try to screw it in,maybe someone who knows this stuff can tell me for sure.
If these will work he said I would want to gap them at .35 sound right?

 

[2texoma]

BR6FS is the correct replacement for MR43T
As for gap,if your ignition coil is seprate from distrubitor cap, .035 is correct. If you have HEI with coil inside dist cap,the gap is much larger.

 

[Studman]

I have the same motor and after reading a ton of online stuff I was told to stick with the AC MR43T of best results.
I did and so far no problems