Skooter -- Yes! The early 261's, made for the '54 and '55 1st series trucks (AD trucks) were the high mount water pumps. As well, any of the crate motors produced after those years and specifically as replacement engines for those trucks will be set up for the high water pump. The casting numbers will be your guide. I have a crate motor 261 in my '49 1-ton. It was out of the '54 mold but built in '59. it required zero modifications to mount in my Advance Design truck. (I used my 216's flywheel and distributor, though, to stay 6 volts).
If you *do* find a later ("crate") engine out of the '54 mold, though ... check the casting numbers and serial number for the actual date of the engine -- at some point (I forget off hand) they changed main bearing styles. Refer to the Tech Tip on rebuilding the 261 for further discussion on this.
John
