Hi Steve, this is what you should have on the front and back engine mount bolt;
a 6mm thick x 22mm outside diameter spacer (washer) between engine and frame,
and a thin washer under the nut (and over the header pipe bracket on the rear bolt).
I have the above standard setup on my rear mount.
On the front mount I have a 'Luftmeister' type anti-vibration dampener kit.
You remove the FRONT 6mm spacers and replace them with 2 thin washers with a rubber dampener in-between.
The dampener is from a David Brown Cone Ring Coupler, part number 0860 1906 (in rubber) or 0037 6006 (urethane). I have the rubber ones, I originally put them in about 20 years ago and have only replaced the rubber ring once, that's how I know the number and where they come from.
Note: the coupler is not from David Brown Tractors, you need to get them from a transmission or engineering supply shop.
The rear mount should be torqued to 65 lb-ft. and the front nuts need to be locktited into place and torqued to 10 - 12 lb-ft.
The engine basically holds the frame tubes in place, if the 6mm spacers are tight to install just prise the frame tube further away from the frame, slip them in and torque it all up again.
Cheers Bruce